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<h1>SQLAlchemy 0.4 Documentation</h1>
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<div id="pagecontrol"><a href="index.html">Multiple Pages</a> | <a href="documentation.html">One Page</a></div>
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<div class="versionheader">Version: 0.4.8 Last Updated: 10/12/08 13:33:19</div>
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<a href="index.html" class="totoc">Table of Contents</a>
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Up: <a href="docstrings.html">API Documentation</a>
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<h2>module sqlalchemy.ext.orderinglist</h2>
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<li><a style="" href="sqlalchemy_ext_orderinglist.html#docstrings_sqlalchemy.ext.orderinglist_modfunc">Module Functions</a></li>
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<li><a style="" href="sqlalchemy_ext_orderinglist.html#docstrings_sqlalchemy.ext.orderinglist_modfunc_ordering_list">ordering_list()</a></li>
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<li><a style="" href="sqlalchemy_ext_orderinglist.html#docstrings_sqlalchemy.ext.orderinglist_OrderingList">class OrderingList(list)</a></li>
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<A name="docstrings_sqlalchemy.ext.orderinglist"></a>
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<div class="sectionL2">
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<h3>module sqlalchemy.ext.orderinglist</h3>
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<div class="darkcell"><p>A custom list that manages index/position information for its children.</p>
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<p><tt class="docutils literal"><span class="pre">orderinglist</span></tt> is a custom list collection implementation for mapped relations
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that keeps an arbitrary "position" attribute on contained objects in sync with
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each object's position in the Python list.</p>
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<p>The collection acts just like a normal Python <tt class="docutils literal"><span class="pre">list</span></tt>, with the added
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behavior that as you manipulate the list (via <tt class="docutils literal"><span class="pre">insert</span></tt>, <tt class="docutils literal"><span class="pre">pop</span></tt>, assignment,
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deletion, what have you), each of the objects it contains is updated as needed
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to reflect its position. This is very useful for managing ordered relations
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which have a user-defined, serialized order:</p>
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<pre class="literal-block">
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from sqlalchemy.ext.orderinglist import ordering_list
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users = Table('users', metadata,
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Column('id', Integer, primary_key=True))
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blurbs = Table('user_top_ten_list', metadata,
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Column('id', Integer, primary_key=True),
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Column('user_id', Integer, ForeignKey('users.id')),
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Column('position', Integer),
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Column('blurb', String(80)))
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class User(object): pass
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def __init__(self, blurb):
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mapper(User, users, properties={
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'topten': relation(Blurb, collection_class=ordering_list('position'),
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order_by=[blurbs.c.position])
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mapper(Blurb, blurbs)
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u.topten.append(Blurb('Number one!'))
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u.topten.append(Blurb('Number two!'))
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assert [blurb.position for blurb in u.topten] == [0, 1]
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# The objects will be renumbered automaticaly after any list-changing
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# operation, for example an insert:
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u.topten.insert(1, Blurb('I am the new Number Two.'))
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assert [blurb.position for blurb in u.topten] == [0, 1, 2]
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assert u.topten[1].blurb == 'I am the new Number Two.'
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assert u.topten[1].position == 1
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<p>Numbering and serialization are both highly configurable. See the docstrings
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in this module and the main SQLAlchemy documentation for more information and
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<p>The <b>ordering_list</b> function is the ORM-compatible
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constructor for OrderingList instances.</p>
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<A name="docstrings_sqlalchemy.ext.orderinglist_modfunc"></a>
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<div class="sectionL3">
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<h3>Module Functions</h3>
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<div class="darkcell">
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<A name="docstrings_sqlalchemy.ext.orderinglist_modfunc_ordering_list"></a>
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<b>def ordering_list(<i>attr</i>, <i>count_from=None</i>, <i>**kw</i>)</b>
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<div class="docstring">
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<p>Prepares an OrderingList factory for use in mapper definitions.</p>
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<p>Returns an object suitable for use as an argument to a Mapper relation's
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<tt class="docutils literal"><span class="pre">collection_class</span></tt> option. Arguments are:</p>
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<dl class="docutils">
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<dd>Name of the mapped attribute to use for storage and retrieval of
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ordering information</dd>
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<dt>count_from (optional)</dt>
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<dd>Set up an integer-based ordering, starting at <tt class="docutils literal"><span class="pre">count_from</span></tt>. For
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example, <tt class="docutils literal"><span class="pre">ordering_list('pos',</span> <span class="pre">count_from=1)</span></tt> would create a 1-based
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list in SQL, storing the value in the 'pos' column. Ignored if
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<tt class="docutils literal"><span class="pre">ordering_func</span></tt> is supplied.</dd>
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<p>Passes along any keyword arguments to <tt class="docutils literal"><span class="pre">OrderingList</span></tt> constructor.</p>
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<A name="docstrings_sqlalchemy.ext.orderinglist_OrderingList"></a>
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<div class="sectionL3">
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<h3>class OrderingList(list)</h3>
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<div class="darkcell"><p>A custom list that manages position information for its children.</p>
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<p>See the module and __init__ documentation for more details. The
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<tt class="docutils literal"><span class="pre">ordering_list</span></tt> function is used to configure <tt class="docutils literal"><span class="pre">OrderingList</span></tt>
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collections in <tt class="docutils literal"><span class="pre">mapper</span></tt> relation definitions.</p>
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<div class="darkcell">
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<b>def __init__(<i>self</i>, <i>ordering_attr=None</i>, <i>ordering_func=None</i>, <i>reorder_on_append=False</i>)</b>
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<div class="docstring">
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<p>A custom list that manages position information for its children.</p>
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<p><tt class="docutils literal"><span class="pre">OrderingList</span></tt> is a <tt class="docutils literal"><span class="pre">collection_class</span></tt> list implementation that
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syncs position in a Python list with a position attribute on the
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<p>This implementation relies on the list starting in the proper order,
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so be <strong>sure</strong> to put an <tt class="docutils literal"><span class="pre">order_by</span></tt> on your relation.</p>
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<dl class="docutils">
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<dt>ordering_attr</dt>
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<dd>Name of the attribute that stores the object's order in the relation.</dd>
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<dt>ordering_func</dt>
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<dd><p class="first">Optional. A function that maps the position in the Python list to a
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value to store in the <tt class="docutils literal"><span class="pre">ordering_attr</span></tt>. Values returned are usually
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(but need not be!) integers.</p>
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<p>An <tt class="docutils literal"><span class="pre">ordering_func</span></tt> is called with two positional parameters: the
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index of the element in the list, and the list itself.</p>
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<p class="last">If omitted, Python list indexes are used for the attribute values.
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Two basic pre-built numbering functions are provided in this module:
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<tt class="docutils literal"><span class="pre">count_from_0</span></tt> and <tt class="docutils literal"><span class="pre">count_from_1</span></tt>. For more exotic examples
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like stepped numbering, alphabetical and Fibonacci numbering, see
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<dt>reorder_on_append</dt>
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<dd><p class="first">Default False. When appending an object with an existing (non-None)
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ordering value, that value will be left untouched unless
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<tt class="docutils literal"><span class="pre">reorder_on_append</span></tt> is true. This is an optimization to avoid a
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variety of dangerous unexpected database writes.</p>
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<p>SQLAlchemy will add instances to the list via append() when your
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object loads. If for some reason the result set from the database
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skips a step in the ordering (say, row '1' is missing but you get
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'2', '3', and '4'), reorder_on_append=True would immediately
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renumber the items to '1', '2', '3'. If you have multiple sessions
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making changes, any of whom happen to load this collection even in
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passing, all of the sessions would try to "clean up" the numbering
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in their commits, possibly causing all but one to fail with a
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concurrent modification error. Spooky action at a distance.</p>
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<p class="last">Recommend leaving this with the default of False, and just call
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<tt class="docutils literal"><span class="pre">_reorder()</span></tt> if you're doing <tt class="docutils literal"><span class="pre">append()</span></tt> operations with
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previously ordered instances or when doing some housekeeping after
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manual sql operations.</p>
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<div class="darkcell">
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<b>def append(<i>self</i>, <i>entity</i>)</b>
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<div class="docstring">
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<div class="darkcell">
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<b>def insert(<i>self</i>, <i>index</i>, <i>entity</i>)</b>
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<div class="docstring">
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<div class="darkcell">
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<b>def pop(<i>self</i>, <i>index=-1</i>)</b>
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<div class="docstring">
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<div class="darkcell">
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<b>def remove(<i>self</i>, <i>entity</i>)</b>
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<div class="docstring">
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<div class="darkcell">
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<b>def __delitem__(<i>self</i>, <i>index</i>)</b>
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<div class="docstring">
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<div class="darkcell">
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<b>def __delslice__(<i>self</i>, <i>start</i>, <i>end</i>)</b>
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<div class="docstring">
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<div class="darkcell">
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<b>def __setitem__(<i>self</i>, <i>index</i>, <i>entity</i>)</b>
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<div class="docstring">
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<div class="darkcell">
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<b>def __setslice__(<i>self</i>, <i>start</i>, <i>end</i>, <i>values</i>)</b>
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<div class="docstring">
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