sqlalchemy-commits Mailing List for SQLAlchemy (Page 374)

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<title>[1107] sqlalchemy/trunk/examples: added backref() function, allows the creation of a backref where you also send keyword arguments that will be placed on the relation</title>
</head>
<body>

<div id="msg">
<dl>
<dt>Revision</dt> <dd>1107</dd>
<dt>Author</dt> <dd>zzzeek</dd>
<dt>Date</dt> <dd>2006-03-06 21:14:08 -0600 (Mon, 06 Mar 2006)</dd>
</dl>

<h3>Log Message</h3>
<pre>added backref() function, allows the creation of a backref where you also send keyword arguments that will be placed on the relation</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#sqlalchemytrunklibsqlalchemymapping__init__py">sqlalchemy/trunk/lib/sqlalchemy/mapping/__init__.py</a></li>
<li><a href="#sqlalchemytrunklibsqlalchemymappingpropertiespy">sqlalchemy/trunk/lib/sqlalchemy/mapping/properties.py</a></li>
</ul>

<h3>Added Paths</h3>
<ul>
<li>sqlalchemy/trunk/examples/backref/</li>
<li><a href="#sqlalchemytrunkexamplesbackrefbackref_treepy">sqlalchemy/trunk/examples/backref/backref_tree.py</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="sqlalchemytrunkexamplesbackrefbackref_treepy"></a>
<div class="addfile"><h4>Added: sqlalchemy/trunk/examples/backref/backref_tree.py (1106 => 1107)</h4>
<pre class="diff"><span>
<span class="info">--- sqlalchemy/trunk/examples/backref/backref_tree.py	2006-03-06 23:15:47 UTC (rev 1106)
+++ sqlalchemy/trunk/examples/backref/backref_tree.py	2006-03-07 03:14:08 UTC (rev 1107)
</span><span class="lines">@@ -0,0 +1,41 @@
</span><ins>+from sqlalchemy import *
+import sqlalchemy.attributes as attributes
+
+engine = create_engine('sqlite://', echo=True)
+
+class Tree(object):
+    def __init__(self, name='', father=None):
+        self.name = name
+        self.father = father
+    def __str__(self):
+        return '&lt;TreeNode: %s&gt;' % self.name
+    def __repr__(self):
+        return self.__str__()
+        
+table = Table('tree', engine,
+              Column('id', Integer, primary_key=True),
+              Column('name', String(64), nullable=False),
+              Column('father_id', Integer, ForeignKey('tree.id'), nullable=True),)
+
+assign_mapper(Tree, table,
+              properties={
+     # set up a backref using a string
+     #'father':relation(Tree, foreignkey=table.c.id,primaryjoin=table.c.father_id==table.c.id,  backref='childs')},
+                
+     # or set up using the backref() function, which allows arguments to be passed
+     'childs':relation(Tree, foreignkey=table.c.father_id, primaryjoin=table.c.father_id==table.c.id,  backref=backref('father', uselist=False, foreignkey=table.c.id))},
+            )
+
+table.create()
+root = Tree('root')
+child1 = Tree('child1', root)
+child2 = Tree('child2', root)
+child3 = Tree('child3', child1)
+
+objectstore.commit()
+
+print root.childs
+print child1.childs
+print child2.childs
+print child2.father
+print child3.father
</ins></span></pre></div>
<a id="sqlalchemytrunklibsqlalchemymapping__init__py"></a>
<div class="modfile"><h4>Modified: sqlalchemy/trunk/lib/sqlalchemy/mapping/__init__.py (1106 => 1107)</h4>
<pre class="diff"><span>
<span class="info">--- sqlalchemy/trunk/lib/sqlalchemy/mapping/__init__.py	2006-03-06 23:15:47 UTC (rev 1106)
+++ sqlalchemy/trunk/lib/sqlalchemy/mapping/__init__.py	2006-03-07 03:14:08 UTC (rev 1107)
</span><span class="lines">@@ -19,7 +19,7 @@
</span><span class="cx"> from properties import *
</span><span class="cx"> import mapper as mapperlib
</span><span class="cx"> 
</span><del>-__all__ = ['relation', 'eagerload', 'lazyload', 'noload', 'deferred', 'defer', 'undefer',
</del><ins>+__all__ = ['relation', 'backref', 'eagerload', 'lazyload', 'noload', 'deferred', 'defer', 'undefer',
</ins><span class="cx">         'mapper', 'clear_mappers', 'objectstore', 'sql', 'extension', 'class_mapper', 'object_mapper', 'MapperExtension',
</span><span class="cx">         'assign_mapper', 'cascade_mappers'
</span><span class="cx">         ]
</span><span class="lines">@@ -39,7 +39,12 @@
</span><span class="cx">     else:
</span><span class="cx">         return EagerLoader(mapper, secondary, primaryjoin, secondaryjoin, **kwargs)
</span><span class="cx"> 
</span><ins>+def backref(name, **kwargs):
+    return BackRef(name, **kwargs)
+    
</ins><span class="cx"> def deferred(*columns, **kwargs):
</span><ins>+    &quot;&quot;&quot;returns a DeferredColumnProperty, which indicates this object attributes should only be loaded 
+    from its corresponding table column when first accessed.&quot;&quot;&quot;
</ins><span class="cx">     return DeferredColumnProperty(*columns, **kwargs)
</span><span class="cx">     
</span><span class="cx"> def mapper(class_, table=None, *args, **params):
</span></span></pre></div>
<a id="sqlalchemytrunklibsqlalchemymappingpropertiespy"></a>
<div class="modfile"><h4>Modified: sqlalchemy/trunk/lib/sqlalchemy/mapping/properties.py (1106 => 1107)</h4>
<pre class="diff"><span>
<span class="info">--- sqlalchemy/trunk/lib/sqlalchemy/mapping/properties.py	2006-03-06 23:15:47 UTC (rev 1106)
+++ sqlalchemy/trunk/lib/sqlalchemy/mapping/properties.py	2006-03-07 03:14:08 UTC (rev 1107)
</span><span class="lines">@@ -136,7 +136,10 @@
</span><span class="cx">             print &quot;'use_alias' argument to relation() is deprecated.  eager loads automatically alias-ize tables now.&quot;
</span><span class="cx">         self.order_by = order_by
</span><span class="cx">         self.attributeext=attributeext
</span><del>-        self.backref = backref
</del><ins>+        if isinstance(backref, str):
+            self.backref = BackRef(backref)
+        else:
+            self.backref = backref
</ins><span class="cx">         self.is_backref = is_backref
</span><span class="cx"> 
</span><span class="cx">     def copy(self):
</span><span class="lines">@@ -197,27 +200,13 @@
</span><span class="cx">             # if a backref name is defined, set up an extension to populate 
</span><span class="cx">             # attributes in the other direction
</span><span class="cx">             if self.backref is not None:
</span><del>-                self.attributeext = attributes.GenericBackrefExtension(self.backref)
</del><ins>+                self.attributeext = self.backref.get_extension()
</ins><span class="cx">         
</span><span class="cx">             # set our class attribute
</span><span class="cx">             self._set_class_attribute(parent.class_, key)
</span><span class="cx"> 
</span><span class="cx">             if self.backref is not None:
</span><del>-                # try to set a LazyLoader on our mapper referencing the parent mapper
-                if not self.mapper.props.has_key(self.backref):
-                    if self.secondaryjoin is not None:
-                        # if setting up a backref to a many-to-many, reverse the order
-                        # of the &quot;primary&quot; and &quot;secondary&quot; joins
-                        pj = self.secondaryjoin
-                        sj = self.primaryjoin
-                    else:
-                        pj = self.primaryjoin
-                        sj = None
-                    self.mapper.add_property(self.backref, LazyLoader(self.parent, self.secondary, pj, sj, backref=self.key, is_backref=True));
-                else:
-                    # else set one of us as the &quot;backreference&quot;
-                    if not self.mapper.props[self.backref].is_backref:
-                        self.is_backref=True
</del><ins>+                self.backref.compile(self)
</ins><span class="cx">         elif not objectstore.global_attributes.is_class_managed(parent.class_, key):
</span><span class="cx">             raise ArgumentError(&quot;Non-primary property created for attribute '%s' on class '%s', but that attribute is not managed! Insure that the primary mapper for this class defines this property&quot; % (key, parent.class_.__name__))
</span><span class="cx"> 
</span><span class="lines">@@ -816,7 +805,33 @@
</span><span class="cx">         kwargs = util.constructor_args(oldprop)
</span><span class="cx">         mapper.set_property(key, class_(**kwargs ))
</span><span class="cx"> 
</span><del>-            
</del><ins>+class BackRef(object):
+    &quot;&quot;&quot;stores the name of a backreference property as well as a relation (PropertyLoader),
+    used to construct more customized backrefs&quot;&quot;&quot;
+    def __init__(self, key, **kwargs):
+        self.key = key
+        self.kwargs = kwargs
+    def compile(self, prop):
+        # try to set a LazyLoader on our mapper referencing the parent mapper
+        if not prop.mapper.props.has_key(self.key):
+            if prop.secondaryjoin is not None:
+                # if setting up a backref to a many-to-many, reverse the order
+                # of the &quot;primary&quot; and &quot;secondary&quot; joins
+                pj = prop.secondaryjoin
+                sj = prop.primaryjoin
+            else:
+                pj = prop.primaryjoin
+                sj = None
+            relation = LazyLoader(prop.parent, prop.secondary, pj, sj, backref=prop.key, is_backref=True, **self.kwargs)
+            prop.mapper.add_property(self.key, relation);
+        else:
+            # else set one of us as the &quot;backreference&quot;
+            if not prop.mapper.props[self.key].is_backref:
+                prop.is_backref=True
+        
+    def get_extension(self):
+        return attributes.GenericBackrefExtension(self.key)
+        
</ins><span class="cx"> class EagerLazyOption(GenericOption):
</span><span class="cx">     &quot;&quot;&quot;an option that switches a PropertyLoader to be an EagerLoader or LazyLoader&quot;&quot;&quot;
</span><span class="cx">     def __init__(self, key, toeager = True, **kwargs):
</span></span></pre>
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