[sqlalchemy] Re: grandparent id relation
On Sep 18, 2:54 pm, Michael Bayer [EMAIL PROTECTED] wrote: 2. more involved: catch change events and populate a Child.grandparent relation(). 0.5 has made the AttributeExtension API public which would be a good place to catch this event. The advantage to this is that your Child has a grandparent already set before any SQL is issued to the database. Thanks Michael, I managed to get 2. to work.. However I was now thinking it may be simpler to create a new relation 'grandchildren' on the grandparent.. and add the new child to both the parent and grandparent parent.children = [child] grandparent.grandchildren = [child] Is there a hook for me to add to the second collection automatically (i.e. an event when object is added to a collection)? Thanks --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com 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 -~--~~~~--~~--~--~---
[sqlalchemy] Re: grandparent id relation
On Sep 19, 2008, at 11:47 AM, GHZ wrote: On Sep 18, 2:54 pm, Michael Bayer [EMAIL PROTECTED] wrote: 2. more involved: catch change events and populate a Child.grandparent relation(). 0.5 has made the AttributeExtension API public which would be a good place to catch this event. The advantage to this is that your Child has a grandparent already set before any SQL is issued to the database. Thanks Michael, I managed to get 2. to work.. However I was now thinking it may be simpler to create a new relation 'grandchildren' on the grandparent.. and add the new child to both the parent and grandparent parent.children = [child] grandparent.grandchildren = [child] Is there a hook for me to add to the second collection automatically (i.e. an event when object is added to a collection)? its all the same idea, collections and scalars fire off events and AttributeExtension lets you catch them. If you put the collection/ attribute on grandparent or child, its pretty much the same thing. the other route to go is to use descriptors and custom collections for this stuff but I think AttributeExtension is simpler. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com 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 -~--~~~~--~~--~--~---
[sqlalchemy] Re: grandparent id relation
On Sep 18, 2008, at 6:27 AM, GHZ wrote:
Hi,
I have a database table : 'Child' that contains the parent_id and
grandparent_id. Foreign keys are present for both.
I'm using declarative
What is best practice to have the grandparent_id column set correctly
when I insert?
class GrandParent(Base):
__tablename__ = 'grandparent'
__table_args__ = {'autoload' : True, 'useexisting' : True}
children = relation('Parent', backref=backref('parents')
class Parent(Base):
__tablename__ = 'parent'
__table_args__ = {'autoload' : True, 'useexisting' : True}
children = relation('Child', backref=backref('parents')
class Child(Base):
# Table has parent_id and grandparent_id columns
__tablename__ = 'child'
__table_args__ = {'autoload' : True, 'useexisting' : True}
grandparent = GrandParent()
parent = Parent()
child = Child()
grandparent.children = [parent]
parent.children = [child]
When I flush, I want child.grandparent_id to be set to the newly
created grandparent.
theres two general ways:
1. quick and dirty: use a before_insert()/before_update()
MapperExtension which sets the grandparent_id column on Child. If
Child also had a relation() to GrandParent, you'd want to expire() it
too.
2. more involved: catch change events and populate a Child.grandparent
relation(). 0.5 has made the AttributeExtension API public which
would be a good place to catch this event. The advantage to this is
that your Child has a grandparent already set before any SQL is
issued to the database.
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