--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/doc/book/en/devrepo/entityclasses/adapters.rst	Mon Jul 05 12:37:21 2010 +0200
@@ -0,0 +1,168 @@
+.. _adapters:
+
+Interfaces and Adapters
+-----------------------
+
+Interfaces are the same thing as object-oriented programming
+`interfaces`_. Adapter refers to a well-known `adapter`_ design
+pattern that helps separating concerns in object oriented
+applications.
+
+.. _`interfaces`: http://java.sun.com/docs/books/tutorial/java/concepts/interface.html
+.. _`adapter`: http://en.wikipedia.org/wiki/Adapter_pattern
+
+In |cubicweb| adapters provide logical functionalities
+to entity types. They are introduced in version `3.9`. Before that one
+had to implements Interfaces in entity classes to achieve a similar goal. However,
+hte problem with this approch is that is clutters the entity class's namespace, exposing
+name collision risks with schema attributes/relations or even methods names
+(different interfaces may define the same method with not necessarily the same
+ behviour expected).
+
+Definition of an adapter is quite trivial. An excerpt from cubicweb
+itself (found in :mod:`cubicweb.entities.adapters`):
+
+.. sourcecode:: python
+
+
+    class ITreeAdapter(EntityAdapter):
+        """This adapter has to be overriden to be configured using the
+        tree_relation, child_role and parent_role class attributes to
+        benefit from this default implementation
+        """
+        __regid__ = 'ITree'
+
+        child_role = 'subject'
+        parent_role = 'object'
+
+        def children_rql(self):
+            """returns RQL to get children """
+            return self.entity.cw_related_rql(self.tree_relation, self.parent_role)
+
+The adapter object has ``self.entity`` attribute which represents the
+entity being adapted.
+
+Specializing and binding an adapter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. sourcecode:: python
+
+  from cubicweb.entities.adapters import ITreeAdapter
+
+  class MyEntityITreeAdapter(ITreeAdapter):
+      __select__ = implements('MyEntity')
+      tree_relation = 'filed_under'
+
+The ITreeAdapter here provides a default implementation. The
+tree_relation class attribute is actually used by this implementation
+to help implement correct behaviour.
+
+Here we provide a specific implementation which will be bound for
+``MyEntity`` entity type (the `adaptee`).
+
+
+Selecting on an adapter
+~~~~~~~~~~~~~~~~~~~~~~~
+
+There is an ``adaptable`` selector which can be used instead of
+``implements``.
+
+.. _interfaces_to_adapters:
+
+Converting code from Interfaces/Mixins to Adapters
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Here we go with a small example. Before:
+
+.. sourcecode:: python
+
+    from cubicweb.selectors import implements
+    from cubicweb.interfaces import ITree
+    from cubicweb.mixins import ITreeMixIn
+
+    class MyEntity(ITreeMixIn, AnyEntity):
+        __implements__ = AnyEntity.__implements__ + (ITree,)
+
+
+    class ITreeView(EntityView):
+        __select__ = implements('ITree')
+        def cell_call(self, row, col):
+            entity = self.cw_rset.get_entity(row, col)
+            children = entity.children()
+
+After:
+
+.. sourcecode:: python
+
+    from cubicweb.selectors import adaptable, implements
+    from cubicweb.entities.adapters import ITreeAdapter
+
+    class MyEntityITreeAdapter(ITreeAdapter):
+        __select__ = implements('MyEntity')
+
+    class ITreeView(EntityView):
+        __select__ = adaptable('ITree')
+        def cell_call(self, row, col):
+            entity = self.cw_rset.get_entity(row, col)
+            itree = entity.cw_adapt_to('ITree')
+            children = itree.children()
+
+As we can see, the interface/mixin duality disappears and the entity
+class itself is completely freed from these concerns. When you want
+to use the ITree interface of an entity, call its `cw_adapt_to` method
+to get an adapter for this interface, then access to members of the
+interface on the adapter
+
+Let's look at an example where we defined everything ourselves. We
+start from:
+
+.. sourcecode:: python
+
+    class IFoo(Interface):
+        def bar(self, *args):
+            raise NotImplementedError
+
+    class MyEntity(AnyEntity):
+        __regid__ = 'MyEntity'
+
+        def bar(self, *args):
+            return sum(captain.age for captain in self.captains)
+
+    class FooView(EntityView):
+       __regid__ = 'mycube.fooview'
+       __select__ = implements('IFoo')
+
+        def cell_call(self, row, col):
+            entity = self.cw_rset.get_entity(row, col)
+            self.w('bar: %s' % entity.bar())
+
+Converting to:
+
+.. sourcecode:: python
+
+   class IFooAdapter(EntityAdapter):
+       __regid__ = 'IFoo'
+
+       def bar(self, *args):
+           return sum(captain.age for captain in self.entity.captains)
+
+   class FooView(EntityView):
+      __regid__ = 'mycube.fooview'
+      __select__ = adaptable('IFoo')
+
+        def cell_call(self, row, col):
+            entity = self.cw_rset.get_entity(row, col)
+            self.w('bar: %s' % entity.cw_adapt_to('IFoo').bar())
+
+.. note::
+
+   When migrating an entity method to an adapter, the code can be moved as is
+   except for the `self` of the entity class, which in the adapter must become `self.entity`.
+
+Adapters defined in the library
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. automodule:: cubicweb.entities.adapters
+   :members:
+
+More are defined in web/views.