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Tangram::Expr - manipulate expressions on database server side
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my ($r1, $r2) = $storage->remote(qw( ... ));
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$r1->{field} operator $value
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$r1->{field} operator $r2->{field2}
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$r1->{collection}->includes( $obj )
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$r1->{collection}->exists( $obj, $filter )
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Tangram::Expr objects represent expressions that will be evaluated on
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the database server side.
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Expression objects fall into one of the following categories: numeric,
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string, reference or collection.
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The methods in Expr are needed only by people extending Tangram. See
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=head1 NUMERIC EXPRESSIONS
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Numeric expression objects can be compared using the operators ==, !=,
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<, >, <= and >=. The other operand must be either another numeric
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expression object, or a normal Perl numeric value. The result of the
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comparison is a Filter.
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=head1 STRING EXPRESSIONS
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String expression objects can be compared using the operators eq, ne,
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lt, gt, le, and ge. The other operand must be either a string
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expression object or any Perl scalar value. Tangram will automatically
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quote the operand as required by the SQL syntax. The result of the
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comparison is a Tangram::Filter.
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String expression objects also support the method like($str), where
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$str is a string that may contain SQL wildcards. The result is a
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Tangram::Filter that translates to a SQL C<LIKE $str> predicate.
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=head1 REFERENCE EXPRESSIONS
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Reference expression objects can be compared for equality using
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operators == and !=. The other operand must be another reference
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expression, a persistent object or undef(). The result of the
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comparison is a Filter.
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=head1 COLLECTION EXPRESSIONS
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Collection expression objects represents a collection inside an
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object. It supports the includes() and exists() methods, which returns
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a Tangram::Filter stating that the collection must contain the
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operand. exists() uses a subselect.
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The operand may be a Tangram::Remote, a persistent object,
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operator < is provided as a synonym for includes().
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Predicate objects represent logical expressions, or
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conditions. Predicates support logical operators &, | and !. Note that
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a I<single> ampersand or vertical bar must be used. The result is
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=head2 new($type, $expr, @remotes)
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Returns a new instance.
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$type is a Type object corresponding to this expression (see
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$expr is a SQL expression. It will eventually become part of a
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@remotes contains the Remote objects (see L<Tangram::Remote>) that
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participate in the expression. Tangram uses this list to insert the
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corresponding tables in the FROM clause and conditions in the
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=head1 INSTANCE METHODS
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Returns the SQL equivalent for this expression.
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Returns the Type (see L<Tangram::Type>) corresponding to this
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Returns the list of the objects that participate in this
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Returns the Storage associated with this expression.
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$person is called 'Homer'
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$person->{name} eq 'Homer'
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$person's name ends with 'mer'
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$person->{name}->like('%mer');
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$person is older than 35
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$person is married to $homer
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$person->{partner} == $homer
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$person is not $homer
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$person is not $homer and is older than 65
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$person != $homer & $person->{age} > 65
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$person is $bart's parent
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$person->{children}->includes( $bart )
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$person->{children} < $bart
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$person is not $bart's parent
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!$person->{children}->includes( $bart )
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!($person->{children} < $bart)
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L<Tangram::Remote>, L<Tangram::Expr>, L<Tangram::Storage>
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Tangram/Expr.pod
