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var DOCUMENTATION_OPTIONS = {

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URL_ROOT: '../../',

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VERSION: '0.8.2',

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VERSION: '0.8.3',

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COLLAPSE_MODINDEX: false,

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FILE_SUFFIX: '.html'

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};

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</div>

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Release: 0.8.2 | Release Date: July 3, 2013

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Release: 0.8.3 | Release Date: October 26, 2013

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</div>

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<h2>Synopsis<a class="headerlink" href="#synopsis" title="Permalink to this headline">¶</a></h2>

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SQLAlchemy object-relational configuration involves the

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combination of <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>, <a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.mapper" title="sqlalchemy.orm.mapper"><tt class="xref py py-func docutils literal">mapper()</tt></a>, and class

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combination of <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>, <a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.mapper" title="sqlalchemy.orm.mapper"><tt class="xref py py-func docutils literal">mapper()</tt></a>, and class

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objects to define a mapped class.

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<a class="reference internal" href="#module-sqlalchemy.ext.declarative" title="sqlalchemy.ext.declarative"><tt class="xref py py-mod docutils literal">declarative</tt></a> allows all three to be

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expressed at once within the class declaration. As much as

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</div>

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Above, the <a class="reference internal" href="#sqlalchemy.ext.declarative.declarative_base" title="sqlalchemy.ext.declarative.declarative_base"><tt class="xref py py-func docutils literal">declarative_base()</tt></a> callable returns a new base class from

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which all mapped classes should inherit. When the class definition is

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completed, a new <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> and <a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.mapper" title="sqlalchemy.orm.mapper"><tt class="xref py py-func docutils literal">mapper()</tt></a> will have been generated.

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completed, a new <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> and <a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.mapper" title="sqlalchemy.orm.mapper"><tt class="xref py py-func docutils literal">mapper()</tt></a> will have been generated.

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The resulting table and mapper are accessible via

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<tt class="docutils literal">__table__</tt> and <tt class="docutils literal">__mapper__</tt> attributes on the

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<tt class="docutils literal">SomeClass</tt> class:

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</div>

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<h2>Defining Attributes<a class="headerlink" href="#defining-attributes" title="Permalink to this headline">¶</a></h2>

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In the previous example, the <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> objects are

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In the previous example, the <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> objects are

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automatically named with the name of the attribute to which they are

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assigned.

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To name columns explicitly with a name distinct from their mapped attribute,

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id = Column("some_table_id", Integer, primary_key=True)</pre></div>

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</div>

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Attributes may be added to the class after its construction, and they will be

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added to the underlying <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> and

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added to the underlying <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> and

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<a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.mapper" title="sqlalchemy.orm.mapper"><tt class="xref py py-func docutils literal">mapper()</tt></a> definitions as appropriate:

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<div class="highlight-python"><div class="highlight"><pre>SomeClass.data = Column('data', Unicode)

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SomeClass.related = relationship(RelatedInfo)</pre></div>

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Classes which are constructed using declarative can interact freely

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with classes that are mapped explicitly with <a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.mapper" title="sqlalchemy.orm.mapper"><tt class="xref py py-func docutils literal">mapper()</tt></a>.

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It is recommended, though not required, that all tables

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share the same underlying <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> object,

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so that string-configured <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.ForeignKey" title="sqlalchemy.schema.ForeignKey"><tt class="xref py py-class docutils literal">ForeignKey</tt></a>

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share the same underlying <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> object,

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so that string-configured <a class="reference internal" href="../../core/constraints.html#sqlalchemy.schema.ForeignKey" title="sqlalchemy.schema.ForeignKey"><tt class="xref py py-class docutils literal">ForeignKey</tt></a>

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references can be resolved without issue.

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</div>

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<h2>Accessing the MetaData<a class="headerlink" href="#accessing-the-metadata" title="Permalink to this headline">¶</a></h2>

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The <a class="reference internal" href="#sqlalchemy.ext.declarative.declarative_base" title="sqlalchemy.ext.declarative.declarative_base"><tt class="xref py py-func docutils literal">declarative_base()</tt></a> base class contains a

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> object where newly defined

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects are collected. This object is

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> object where newly defined

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects are collected. This object is

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intended to be accessed directly for

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a>-specific operations. Such as, to issue

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a>-specific operations. Such as, to issue

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CREATE statements for all tables:

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<div class="highlight-python"><div class="highlight"><pre>engine = create_engine('sqlite://')

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Base.metadata.create_all(engine)</pre></div>

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</div>

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<a class="reference internal" href="#sqlalchemy.ext.declarative.declarative_base" title="sqlalchemy.ext.declarative.declarative_base"><tt class="xref py py-func docutils literal">declarative_base()</tt></a> can also receive a pre-existing

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> object, which allows a

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> object, which allows a

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declarative setup to be associated with an already

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existing traditional collection of <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>

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existing traditional collection of <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>

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objects:

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<div class="highlight-python"><div class="highlight"><pre>mymetadata = MetaData()

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Base = declarative_base(metadata=mymetadata)</pre></div>

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evaluated as Python expressions. The full namespace available within

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this evaluation includes all classes mapped for this declarative base,

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as well as the contents of the <tt class="docutils literal">sqlalchemy</tt> package, including

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expression functions like <a class="reference internal" href="../../core/expression_api.html#sqlalchemy.sql.expression.desc" title="sqlalchemy.sql.expression.desc"><tt class="xref py py-func docutils literal">desc()</tt></a> and

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<a class="reference internal" href="../../core/expression_api.html#sqlalchemy.sql.expression.func" title="sqlalchemy.sql.expression.func"><tt class="xref py py-attr docutils literal">func</tt></a>:

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expression functions like <a class="reference internal" href="../../core/sqlelement.html#sqlalchemy.sql.expression.desc" title="sqlalchemy.sql.expression.desc"><tt class="xref py py-func docutils literal">desc()</tt></a> and

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<a class="reference internal" href="../../core/sqlelement.html#sqlalchemy.sql.expression.func" title="sqlalchemy.sql.expression.func"><tt class="xref py py-attr docutils literal">func</tt></a>:

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<div class="highlight-python"><div class="highlight"><pre>class User(Base):

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# ....

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addresses = relationship("Address",

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primaryjoin="address.Address.user_id=="

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"User.id")</pre></div>

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</div>

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New in version 0.8: module-qualified paths can be used when specifying string arguments

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New in version 0.8: module-qualified paths can be used when specifying string arguments

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with Declarative, in order to specify specific modules.

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</div>

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Two alternatives also exist to using string-based attributes. A lambda

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can also be used, which will be evaluated after all mappers have been

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configured:

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with declarative as with traditional mappings. The

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<tt class="docutils literal">secondary</tt> argument to

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<a class="reference internal" href="../relationships.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><tt class="xref py py-func docutils literal">relationship()</tt></a> is as usual passed a

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> object, which is typically declared in the

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traditional way. The <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> usually shares

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the <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> object used by the declarative base:

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> object, which is typically declared in the

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traditional way. The <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> usually shares

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the <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> object used by the declarative base:

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<div class="highlight-python"><div class="highlight"><pre>keywords = Table(

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'keywords', Base.metadata,

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Column('author_id', Integer, ForeignKey('authors.id')),

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keywords = relationship("Keyword", secondary="keywords")</pre></div>

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</div>

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As with traditional mapping, its generally not a good idea to use

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a <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> as the “secondary” argument which is also mapped to

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a <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> as the “secondary” argument which is also mapped to

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a class, unless the <a class="reference internal" href="../relationships.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><tt class="xref py py-func docutils literal">relationship()</tt></a> is declared with <tt class="docutils literal">viewonly=True</tt>.

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Otherwise, the unit-of-work system may attempt duplicate INSERT and

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DELETE statements against the underlying table.

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arguments are specified using the <tt class="docutils literal">__table_args__</tt> class attribute.

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This attribute accommodates both positional as well as keyword

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arguments that are normally sent to the

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> constructor.

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> constructor.

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The attribute can be specified in one of two forms. One is as a

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dictionary:

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<div class="highlight-python"><div class="highlight"><pre>class MyClass(Base):

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<h2>Using a Hybrid Approach with __table__<a class="headerlink" href="#using-a-hybrid-approach-with-table" title="Permalink to this headline">¶</a></h2>

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As an alternative to <tt class="docutils literal">__tablename__</tt>, a direct

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> construct may be used. The

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> objects, which in this case require

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> construct may be used. The

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> objects, which in this case require

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their names, will be added to the mapping just like a regular mapping

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to a table:

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<div class="highlight-python"><div class="highlight"><pre>class MyClass(Base):

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</div>

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Some configuration schemes may find it more appropriate to use <tt class="docutils literal">__table__</tt>,

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such as those which already take advantage of the data-driven nature of

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> to customize and/or automate schema definition.

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> to customize and/or automate schema definition.

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Note that when the <tt class="docutils literal">__table__</tt> approach is used, the object is immediately

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usable as a plain <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> within the class declaration body itself,

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usable as a plain <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> within the class declaration body itself,

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as a Python class is only another syntactical block. Below this is illustrated

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by using the <tt class="docutils literal">id</tt> column in the <tt class="docutils literal">primaryjoin</tt> condition of a

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<a class="reference internal" href="../relationships.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><tt class="xref py py-func docutils literal">relationship()</tt></a>:

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</div>

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<h2>Using Reflection with Declarative<a class="headerlink" href="#using-reflection-with-declarative" title="Permalink to this headline">¶</a></h2>

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It’s easy to set up a <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> that uses <tt class="docutils literal">autoload=True</tt>

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It’s easy to set up a <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> that uses <tt class="docutils literal">autoload=True</tt>

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in conjunction with a mapped class:

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<div class="highlight-python"><div class="highlight"><pre>class MyClass(Base):

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__table__ = Table('mytable', Base.metadata,

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Base.prepare(e)</pre></div>

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</div>

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New in version 0.8: Added <a class="reference internal" href="#sqlalchemy.ext.declarative.DeferredReflection" title="sqlalchemy.ext.declarative.DeferredReflection"><tt class="xref py py-class docutils literal">DeferredReflection</tt></a>.

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New in version 0.8: Added <a class="reference internal" href="#sqlalchemy.ext.declarative.DeferredReflection" title="sqlalchemy.ext.declarative.DeferredReflection"><tt class="xref py py-class docutils literal">DeferredReflection</tt></a>.

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</div>

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</div>

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<h2>Mapper Configuration<a class="headerlink" href="#mapper-configuration" title="Permalink to this headline">¶</a></h2>

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primary_key=True)

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primary_language = Column(String(50))</pre></div>

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</div>

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Changed in version 0.7: joined table inheritance favors the subclass

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Changed in version 0.7: joined table inheritance favors the subclass

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column over that of the superclass, such as querying above

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for <tt class="docutils literal">Engineer.id</tt>. Prior to 0.7 this was the reverse.

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</div>

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</div>

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<h3>Single Table Inheritance<a class="headerlink" href="#single-table-inheritance" title="Permalink to this headline">¶</a></h3>

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Single table inheritance is defined as a subclass that does not have

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In a situation like this, Declarative can’t be sure

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of the intent, especially if the <tt class="docutils literal">start_date</tt> columns had, for example,

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different types. A situation like this can be resolved by using

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<a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> to define the <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> conditionally, taking

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<a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> to define the <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> conditionally, taking

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care to return the existing column via the parent <tt class="docutils literal">__table__</tt> if it

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already exists:

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<div class="highlight-python"><div class="highlight"><pre>from sqlalchemy.ext.declarative import declared_attr

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</div>

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Above, when <tt class="docutils literal">Manager</tt> is mapped, the <tt class="docutils literal">start_date</tt> column is

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already present on the <tt class="docutils literal">Person</tt> class. Declarative lets us return

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that <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> as a result in this case, where it knows to skip

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that <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> as a result in this case, where it knows to skip

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re-assigning the same column. If the mapping is mis-configured such

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that the <tt class="docutils literal">start_date</tt> column is accidentally re-assigned to a

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different table (such as, if we changed <tt class="docutils literal">Manager</tt> to be joined

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inheritance without fixing <tt class="docutils literal">start_date</tt>), an error is raised which

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indicates an existing <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> is trying to be re-assigned to

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a different owning <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>.

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New in version 0.8: <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> can be used on a non-mixin

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class, and the returned <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> or other mapped attribute

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indicates an existing <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> is trying to be re-assigned to

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a different owning <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>.

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New in version 0.8: <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> can be used on a non-mixin

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class, and the returned <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> or other mapped attribute

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will be applied to the mapping as any other attribute. Previously,

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the resulting attribute would be ignored, and also result in a warning

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being emitted when a subclass was created.

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New in version 0.8: <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a>, when used either with a

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</div>

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New in version 0.8: <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a>, when used either with a

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mixin or non-mixin declarative class, can return an existing

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> already assigned to the parent <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>,

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to indicate that the re-assignment of the <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> should be

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> already assigned to the parent <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>,

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to indicate that the re-assignment of the <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> should be

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skipped, however should still be mapped on the target class,

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in order to resolve duplicate column conflicts.

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</div>

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The same concept can be used with mixin classes (see

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<a class="reference internal" href="#declarative-mixins">Mixin and Custom Base Classes</a>):

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<div class="highlight-python"><div class="highlight"><pre>class Person(Base):

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Because we’re using single table inheritance, we’re sure that in this case,

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<tt class="docutils literal">cls.__table__</tt> refers to <tt class="docutils literal">People.__table__</tt>. If we were mixing joined-

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and single-table inheritance, we might want our mixin to check more carefully

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if <tt class="docutils literal">cls.__table__</tt> is really the <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> we’re looking for.

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if <tt class="docutils literal">cls.__table__</tt> is really the <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> we’re looking for.

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</div>

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</div>

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</div>

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Usage of an abstract base class is a little less straightforward as it

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requires usage of <a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.util.polymorphic_union" title="sqlalchemy.orm.util.polymorphic_union"><tt class="xref py py-func docutils literal">polymorphic_union()</tt></a>,

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which needs to be created with the <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects

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which needs to be created with the <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects

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before the class is built:

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<div class="highlight-python"><div class="highlight"><pre>engineers = Table('engineers', Base.metadata,

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Column('id', Integer, primary_key=True),

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Helper classes provides a simpler pattern for concrete inheritance.

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With these objects, the <tt class="docutils literal">__declare_last__</tt> helper is used to configure the

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“polymorphic” loader for the mapper after all subclasses have been declared.

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New in version 0.7.3.

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New in version 0.7.3.

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</div>

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An abstract base can be declared using the

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<a class="reference internal" href="#sqlalchemy.ext.declarative.AbstractConcreteBase" title="sqlalchemy.ext.declarative.AbstractConcreteBase"><tt class="xref py py-class docutils literal">AbstractConcreteBase</tt></a> class:

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<div class="highlight-python"><div class="highlight"><pre>from sqlalchemy.ext.declarative import AbstractConcreteBase

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and <tt class="docutils literal">b.c.id</tt> are two distinct Python objects, referencing their

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parent tables <tt class="docutils literal">a</tt> and <tt class="docutils literal">b</tt> respectively.

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In the case of the mixin column, it seems that only one

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> object is explicitly created, yet the ultimate

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> object is explicitly created, yet the ultimate

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<tt class="docutils literal">created_at</tt> column above must exist as a distinct Python object

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for each separate destination class. To accomplish this, the declarative

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extension creates a copy of each <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> object encountered on

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extension creates a copy of each <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> object encountered on

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a class that is detected as a mixin.

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This copy mechanism is limited to simple columns that have no foreign

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keys, as a <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.ForeignKey" title="sqlalchemy.schema.ForeignKey"><tt class="xref py py-class docutils literal">ForeignKey</tt></a> itself contains references to columns

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keys, as a <a class="reference internal" href="../../core/constraints.html#sqlalchemy.schema.ForeignKey" title="sqlalchemy.schema.ForeignKey"><tt class="xref py py-class docutils literal">ForeignKey</tt></a> itself contains references to columns

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which can’t be properly recreated at this level. For columns that

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have foreign keys, as well as for the variety of mapper-level constructs

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that require destination-explicit context, the

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</div>

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Where above, the <tt class="docutils literal">address_id</tt> class-level callable is executed at the

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point at which the <tt class="docutils literal">User</tt> class is constructed, and the declarative

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extension can use the resulting <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> object as returned by

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extension can use the resulting <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal">Column</tt></a> object as returned by

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the method without the need to copy it.

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Changed in version >: 0.6.5

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Changed in version >: 0.6.5

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Rename 0.6.5 <tt class="docutils literal">sqlalchemy.util.classproperty</tt>

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into <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a>.

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</div>

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Columns generated by <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> can also be

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referenced by <tt class="docutils literal">__mapper_args__</tt> to a limited degree, currently

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by <tt class="docutils literal">polymorphic_on</tt> and <tt class="docutils literal">version_id_col</tt>, by specifying the

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</div>

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Above, the <tt class="docutils literal">HasStringCollection</tt> mixin produces a <a class="reference internal" href="../relationships.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><tt class="xref py py-func docutils literal">relationship()</tt></a>

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which refers to a newly generated class called <tt class="docutils literal">StringAttribute</tt>. The

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<tt class="docutils literal">StringAttribute</tt> class is generated with it’s own <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>

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<tt class="docutils literal">StringAttribute</tt> class is generated with it’s own <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>

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definition which is local to the parent class making usage of the

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<tt class="docutils literal">HasStringCollection</tt> mixin. It also produces an <a class="reference internal" href="associationproxy.html#sqlalchemy.ext.associationproxy.association_proxy" title="sqlalchemy.ext.associationproxy.association_proxy"><tt class="xref py py-func docutils literal">association_proxy()</tt></a>

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object which proxies references to the <tt class="docutils literal">strings</tt> attribute onto the <tt class="docutils literal">value</tt>

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<a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> decorator must be used so that a distinct

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<a class="reference internal" href="associationproxy.html#sqlalchemy.ext.associationproxy.association_proxy" title="sqlalchemy.ext.associationproxy.association_proxy"><tt class="xref py py-func docutils literal">association_proxy()</tt></a> object is created for each of the <tt class="docutils literal">TypeA</tt>

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and <tt class="docutils literal">TypeB</tt> classes.

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New in version 0.8: <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> is usable with non-mapped

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New in version 0.8: <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> is usable with non-mapped

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attributes, including user-defined attributes as well as

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<a class="reference internal" href="associationproxy.html#sqlalchemy.ext.associationproxy.association_proxy" title="sqlalchemy.ext.associationproxy.association_proxy"><tt class="xref py py-func docutils literal">association_proxy()</tt></a>.

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</div>

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</div>

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<h3>Controlling table inheritance with mixins<a class="headerlink" href="#controlling-table-inheritance-with-mixins" title="Permalink to this headline">¶</a></h3>

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The <tt class="docutils literal">__tablename__</tt> attribute in conjunction with the hierarchy of

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</div>

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<h3>Creating Indexes with Mixins<a class="headerlink" href="#creating-indexes-with-mixins" title="Permalink to this headline">¶</a></h3>

1221

To define a named, potentially multicolumn <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Index" title="sqlalchemy.schema.Index"><tt class="xref py py-class docutils literal">Index</tt></a> that applies to all

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tables derived from a mixin, use the “inline” form of <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Index" title="sqlalchemy.schema.Index"><tt class="xref py py-class docutils literal">Index</tt></a> and

1229

To define a named, potentially multicolumn <a class="reference internal" href="../../core/constraints.html#sqlalchemy.schema.Index" title="sqlalchemy.schema.Index"><tt class="xref py py-class docutils literal">Index</tt></a> that applies to all

1230

tables derived from a mixin, use the “inline” form of <a class="reference internal" href="../../core/constraints.html#sqlalchemy.schema.Index" title="sqlalchemy.schema.Index"><tt class="xref py py-class docutils literal">Index</tt></a> and

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establish it as part of <tt class="docutils literal">__table_args__</tt>:

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<div class="highlight-python"><div class="highlight"><pre>class MyMixin(object):

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a = Column(Integer)

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""

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# do something with mappings</pre></div>

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</div>

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New in version 0.7.3.

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New in version 0.7.3.

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</div>

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</div>

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<h3><tt class="docutils literal">__abstract__</tt><a class="headerlink" href="#abstract" title="Permalink to this headline">¶</a></h3>

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""</pre></div>

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</div>

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One possible use of <tt class="docutils literal">__abstract__</tt> is to use a distinct

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> for different bases:

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> for different bases:

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<div class="highlight-python"><div class="highlight"><pre>Base = declarative_base()

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class DefaultBase(Base):

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metadata = MetaData()</pre></div>

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</div>

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Above, classes which inherit from <tt class="docutils literal">DefaultBase</tt> will use one

1287

<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> as the registry of tables, and those which inherit from

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.MetaData" title="sqlalchemy.schema.MetaData"><tt class="xref py py-class docutils literal">MetaData</tt></a> as the registry of tables, and those which inherit from

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<tt class="docutils literal">OtherBase</tt> will use a different one. The tables themselves can then be

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created perhaps within distinct databases:

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<div class="highlight-python"><div class="highlight"><pre>DefaultBase.metadata.create_all(some_engine)

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OtherBase.metadata_create_all(some_other_engine)</pre></div>

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</div>

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New in version 0.7.3.

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New in version 0.7.3.

1304

</div>

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</div>

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</div>

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<h2>Sessions<a class="headerlink" href="#sessions" title="Permalink to this headline">¶</a></h2>

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Note that <tt class="docutils literal">declarative</tt> does nothing special with sessions, and is

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only intended as an easier way to configure mappers and

1309

<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects. A typical application

1319

<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects. A typical application

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setup using <tt class="xref py py-class docutils literal">scoped_session</tt> might look like:

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<div class="highlight-python"><div class="highlight"><pre>engine = create_engine('postgresql://scott:tiger@localhost/test')

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Session = scoped_session(sessionmaker(autocommit=False,

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<h2>API Reference<a class="headerlink" href="#api-reference" title="Permalink to this headline">¶</a></h2>

1322

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<tt class="descclassname">sqlalchemy.ext.declarative.</tt><tt class="descname">declarative_base</tt><big>(</big>bind=None, metadata=None, mapper=None, cls=<type 'object'>, name='Base', constructor=<function __init__ at 0x10aadd938>, class_registry=None, metaclass=<class 'sqlalchemy.ext.declarative.api.DeclarativeMeta'><big>)</big><a class="headerlink" href="#sqlalchemy.ext.declarative.declarative_base" title="Permalink to this definition">¶</a></dt>

1334

<tt class="descclassname">sqlalchemy.ext.declarative.</tt><tt class="descname">declarative_base</tt><big>(</big>bind=None, metadata=None, mapper=None, cls=<type 'object'>, name='Base', constructor=<function __init__ at 0x10d468140>, class_registry=None, metaclass=<class 'sqlalchemy.ext.declarative.api.DeclarativeMeta'><big>)</big><a class="headerlink" href="#sqlalchemy.ext.declarative.declarative_base" title="Permalink to this definition">¶</a></dt>

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<dd>Construct a base class for declarative class definitions.

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The new base class will be given a metaclass that produces

1327

appropriate <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects and makes

1337

appropriate <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects and makes

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the appropriate <a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.mapper" title="sqlalchemy.orm.mapper"><tt class="xref py py-func docutils literal">mapper()</tt></a> calls based on the

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information provided declaratively in the class and any subclasses

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of the class.

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the <tt class="docutils literal">bind</tt> attribute on the <tt class="xref py py-class docutils literal">MetaData</tt>

1339

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instance.</li>

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<li>metadata – An optional <tt class="xref py py-class docutils literal">MetaData</tt> instance. All

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<a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects implicitly declared by

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<a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> objects implicitly declared by

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subclasses of the base will share this MetaData. A MetaData instance

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will be created if none is provided. The

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<tt class="xref py py-class docutils literal">MetaData</tt> instance will be available via the

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</tr>

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</tbody>

1372

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</table>

1383

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See also

1385

<a class="reference internal" href="#sqlalchemy.ext.declarative.as_declarative" title="sqlalchemy.ext.declarative.as_declarative"><tt class="xref py py-func docutils literal">as_declarative()</tt></a>

1386

</div>

1387

</dd></dl>

1388

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<tt class="descclassname">sqlalchemy.ext.declarative.</tt><tt class="descname">as_declarative</tt><big>(</big>**kw<big>)</big><a class="headerlink" href="#sqlalchemy.ext.declarative.as_declarative" title="Permalink to this definition">¶</a></dt>

1392

<dd>Class decorator for <a class="reference internal" href="#sqlalchemy.ext.declarative.declarative_base" title="sqlalchemy.ext.declarative.declarative_base"><tt class="xref py py-func docutils literal">declarative_base()</tt></a>.

1393

Provides a syntactical shortcut to the <tt class="docutils literal">cls</tt> argument

1394

sent to <a class="reference internal" href="#sqlalchemy.ext.declarative.declarative_base" title="sqlalchemy.ext.declarative.declarative_base"><tt class="xref py py-func docutils literal">declarative_base()</tt></a>, allowing the base class

1395

to be converted in-place to a “declarative” base:

1396

<div class="highlight-python"><pre>from sqlalchemy.ext.declarative import as_declarative

1397

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@as_declarative()

1399

class Base(object)

1400

@declared_attr

1401

def __tablename__(cls):

1402

return cls.__name__.lower()

1403

id = Column(Integer, primary_key=True)

1404

1405

class MyMappedClass(Base):

1406

# ...</pre>

1407

</div>

1408

All keyword arguments passed to <a class="reference internal" href="#sqlalchemy.ext.declarative.as_declarative" title="sqlalchemy.ext.declarative.as_declarative"><tt class="xref py py-func docutils literal">as_declarative()</tt></a> are passed

1409

along to <a class="reference internal" href="#sqlalchemy.ext.declarative.declarative_base" title="sqlalchemy.ext.declarative.declarative_base"><tt class="xref py py-func docutils literal">declarative_base()</tt></a>.

1410

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New in version 0.8.3.

1412

</div>

1413

1414

See also

1415

<a class="reference internal" href="#sqlalchemy.ext.declarative.declarative_base" title="sqlalchemy.ext.declarative.declarative_base"><tt class="xref py py-func docutils literal">declarative_base()</tt></a>

1416

</div>

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</dd></dl>

1374

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1375

1419

1376

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1377

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class <tt class="descclassname">sqlalchemy.ext.declarative.</tt><tt class="descname">declared_attr</tt><big>(</big>fget, *arg, **kw<big>)</big><a class="headerlink" href="#sqlalchemy.ext.declarative.declared_attr" title="Permalink to this definition">¶</a></dt>

1378

<dd>Mark a class-level method as representing the definition of

1422

<dd>Bases: <tt class="xref py py-class docutils literal">sqlalchemy.orm.interfaces._MappedAttribute</tt>, <tt class="xref py py-class docutils literal">__builtin__.property</tt>

1423

Mark a class-level method as representing the definition of

1379

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a mapped property or special declarative member name.

1380

1425

@declared_attr turns the attribute into a scalar-like

1381

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property that can be invoked from the uninstantiated class.

1414

1459

else:

1415

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return {"polymorphic_identity":cls.__name__}</pre></div>

1416

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</div>

1417

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Changed in version 0.8: <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> can be used with

1462

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Changed in version 0.8: <a class="reference internal" href="#sqlalchemy.ext.declarative.declared_attr" title="sqlalchemy.ext.declarative.declared_attr"><tt class="xref py py-class docutils literal">declared_attr</tt></a> can be used with

1419

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non-ORM or extension attributes, such as user-defined attributes

1420

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or <a class="reference internal" href="associationproxy.html#sqlalchemy.ext.associationproxy.association_proxy" title="sqlalchemy.ext.associationproxy.association_proxy"><tt class="xref py py-func docutils literal">association_proxy()</tt></a> objects, which will be assigned

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to the class at class construction time.

1467

</div>

1422

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</dd></dl>

1423

1469

1424

1470

1486

1532

1487

1533

1488

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class <tt class="descclassname">sqlalchemy.ext.declarative.</tt><tt class="descname">AbstractConcreteBase</tt><a class="headerlink" href="#sqlalchemy.ext.declarative.AbstractConcreteBase" title="Permalink to this definition">¶</a></dt>

1489

<dd>A helper class for ‘concrete’ declarative mappings.

1535

<dd>Bases: <tt class="xref py py-class docutils literal">sqlalchemy.ext.declarative.api.ConcreteBase</tt>

1536

A helper class for ‘concrete’ declarative mappings.

1490

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<a class="reference internal" href="#sqlalchemy.ext.declarative.AbstractConcreteBase" title="sqlalchemy.ext.declarative.AbstractConcreteBase"><tt class="xref py py-class docutils literal">AbstractConcreteBase</tt></a> will use the <a class="reference internal" href="../mapper_config.html#sqlalchemy.orm.util.polymorphic_union" title="sqlalchemy.orm.util.polymorphic_union"><tt class="xref py py-func docutils literal">polymorphic_union()</tt></a>

1491

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function automatically, against all tables mapped as a subclass

1492

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to this class. The function is called via the

1552

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<dd>A helper class for construction of mappings based on

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a deferred reflection step.

1554

1601

Normally, declarative can be used with reflection by

1555

setting a <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> object using autoload=True

1602

setting a <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> object using autoload=True

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as the <tt class="docutils literal">__table__</tt> attribute on a declarative class.

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The caveat is that the <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> must be fully

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The caveat is that the <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a> must be fully

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reflected, or at the very least have a primary key column,

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at the point at which a normal declarative mapping is

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constructed, meaning the <a class="reference internal" href="../../core/connections.html#sqlalchemy.engine.Engine" title="sqlalchemy.engine.Engine"><tt class="xref py py-class docutils literal">Engine</tt></a> must be available

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at class declaration time.

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The <a class="reference internal" href="#sqlalchemy.ext.declarative.DeferredReflection" title="sqlalchemy.ext.declarative.DeferredReflection"><tt class="xref py py-class docutils literal">DeferredReflection</tt></a> mixin moves the construction

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of mappers to be at a later point, after a specific

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method is called which first reflects all <a class="reference internal" href="../../core/schema.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>

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method is called which first reflects all <a class="reference internal" href="../../core/metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal">Table</tt></a>

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objects created so far. Classes can define it as such:

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<div class="highlight-python"><div class="highlight"><pre>from sqlalchemy.ext.declarative import declarative_base

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from sqlalchemy.ext.declarative import DeferredReflection

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<div class="highlight-python"><div class="highlight"><pre>ReflectedOne.prepare(engine_one)

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ReflectedTwo.prepare(engine_two)</pre></div>

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</div>

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New in version 0.8.

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New in version 0.8.

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</div>

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</dd></dl>

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</div>

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Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3.

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Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.2b1.

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</div>

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</div>

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