[migration] avoid AssertionError / crashes if migration script is neither a py nor a sql file
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))