Hi!
I have a tree structure modeled into a database using adjacency-list
paradigm (so having a reference to the parent).
class Node(Base):
id = Column(Integer, primary_key=True)
name = Column(String(120))
parent_id = Column(Integer, ForeignKey('id'))
I'm adding some custom relationships like "ancestors", which should give me
the full list of ancestors until the root of the tree.
For implementing this, I am trying to create a viewonly relationship which
shall be empty until I manually load it (because the join conditions are
too difficult to specify at the relationship constructor).
So, I define a "fake" relationship:
ancestors = relationship(Node, viewonly=True, uselist=False,
lazy="noload")
When I load Node instances from the database, this collection is empty. OK.
But I can force the collection to be loaded using contains_eager. Something
like this:
Parent = aliased(Node)
node = session.query(Node)...(complex join
ommited)...options(contains_eager('ancestors', alias=Parent)).one()
Then, if the node WAS NOT on the identity_map, the collection is loaded
successfully. GREAT!
node.ancestors = InstrumentedList([.........])
But, if the node was already in the identity_map, the collection is not
touched, and remains empty :(
node.ancestors = InstrumentedList([])
I am beginning to think that this may be the expected behaviour, as when
the new instance is retrieved from the database, if the identity_key is the
same as one from the identity_map, it is returning that instance from the
identity_map, without touching anything. Is it so?
One final comment. With the contains_eager query, the instances that are
part of the collection are retrieved from the database but not stored on
the identity_map. Is that also the expected behaviour, isn't it?
Thank you very much!
--
----------------------------------
Pau Tallada Crespí
Dep. d'Astrofísica i Cosmologia
Port d'Informació Científica (PIC)
Tel: +34 93 586 8233
----------------------------------
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
