+
−
+
−Class `TreeMixIn`
+
−-----------------
+
−
+
−This class provides a tree interface. This mixin has to be inherited 
+
−explicitly and configured using the tree_attribute, parent_target and 
+
−children_target class attribute to benefit from this default implementation.
+
−
+
−This class provides the following methods:
+
−
+
−  * `different_type_children(entities=True)`, returns children entities
+
−    of different type as this entity. According to the `entities` parameter, 
+
−    returns entity objects (if entity=True) or the equivalent result set.
+
−
+
−  * `same_type_children(entities=True)`, returns children entities of 
+
−    the same type as this entity. According to the `entities` parameter, 
+
−    return entity objects (if entity=True) or the equivalent result set.
+
−  
+
−  * `iterchildren( _done=None)`, iters on the children of the entity.
+
−  
+
−  * `prefixiter( _done=None)`
+
−  
+
−  * `path()`, returns the list of eids from the root object to this object.
+
−  
+
−  * `iterparents()`, iters on the parents of the entity.
+
−  
+
−  * `notification_references(view)`, used to control References field 
+
−    of email send on notification for this entity. `view` is the notification view.
+
−    Should return a list of eids which can be used to generate message ids
+
−    of previously sent email.
+
−
+
−`TreeMixIn` implements also the ITree interface (``cubicweb.interfaces``):
+
−
+
−  * `parent()`, returns the parent entity if any, else None (e.g. if we are on the
+
−    root)
+
−
+
−  * `children(entities=True, sametype=False)`, returns children entities
+
−    according to the `entities` parameter, return entity objects or the
+
−    equivalent result set.
+
−
+
−  * `children_rql()`, returns the RQL query corresponding to the children
+
−    of the entity.
+
−
+
−  * `is_leaf()`, returns True if the entity does not have any children.
+
−
+
−  * `is_root()`, returns True if the entity does not have any parent.
+
−
+
−  * `root()`, returns the root object of the tree representation of
+
−    the entity and its related entities.
+
−
+
−Example of use
+
−``````````````
+
−
+
−Imagine you defined three types of entities in your schema, and they
+
−relates to each others as follows in ``schema.py``::
+
−
+
−  class Entity1(EntityType):
+
−      title = String()
+
−      is_related_to = SubjectRelation('Entity2', 'subject')
+
−
+
−  class Entity2(EntityType):
+
−      title = String()
+
−      belongs_to = SubjectRelation('Entity3', 'subject')
+
−
+
−  class Entity3(EntityType):
+
−      name = String()
+
−
+
−You would like to create a view that applies to both entity types
+
−`Entity1` and `Entity2` and which lists the entities they are related to.
+
−That means when you view `Entity1` you want to list all `Entity2`, and
+
−when you view `Entity2` you want to list all `Entity3`.
+
−
+
−In ``entities.py``::
+
−
+
−  class Entity1(TreeMixIn, AnyEntity):
+
−      id = 'Entity1'
+
−      __implements__ = AnyEntity.__implements__ + (ITree,)
+
−      __rtags__ = {('is_related_to', 'Entity2', 'object'): 'link'}
+
−      tree_attribute = 'is_related_to'
+
−
+
−      def children(self, entities=True):
+
−          return self.different_type_children(entities)
+
−
+
−  class Entity2(TreeMixIn, AnyEntity):
+
−      id = 'Entity2'
+
−      __implements__ = AnyEntity.__implements__ + (ITree,)
+
−      __rtags__ = {('belongs_to', 'Entity3', 'object'): 'link'}
+
−      tree_attribute = 'belongs_to'
+
−
+
−      def children(self, entities=True):
+
−          return self.different_type_children(entities)
+
−
+
−Once this is done, you can define your common view as follows::
+
−
+
−  class E1E2CommonView(baseviews.PrimaryView):
+
−      accepts = ('Entity11, 'Entity2')
+
−      
+
−      def render_entity_relations(self, entity, siderelations):
+
−          self.wview('list', entity.children(entities=False))
+
−