[sqlalchemy] Re: backref relation is None instead of list?

[Dan Eloff]

On 9/9/07, Michael Bayer [EMAIL PROTECTED] wrote:
 I cant reproduce this, although the error to me seems like you are
 actually saying c._parent = [] (some list object).  If thats not it,
 send along a reproducing test script.

I tried to recreate it in the shell and failed.

I then loaded my application, changed _parents to parent and it just
worked. I don't think the change did it, I think it just disappeared
(maybe the reboot?) If it happens again I'll post it on this mailing
list.

Thanks for the tip about one-to-many relations, I was hoping they
worked like that, but when I got the errors I assumed it must not.

Sorry for the false alarm,

-Dan

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[sqlalchemy] Re: backref relation is None instead of list?

[Michael Bayer]

On Sep 9, 2007, at 7:00 PM, Dan Eloff wrote:


 Hi All,

 Table Categories:

 categories_table = sa.Table('categories', connection.metadata)
 [categories_table.append_column(c) for c in (
 sa.Column('id', sa.Integer, primary_key=True),
 sa.Column('name', sa.String(40)),
 sa.Column('flags', sa.SmallInteger),
 sa.Column('parent_id', sa.Integer, sa.ForeignKey 
 ('categories.id')))]

 sa.orm.mapper(Category, categories_table, properties={
 'subcategories' : sa.orm.relation(Category,
 backref=sa.orm.backref('_parent',
 remote_side=[categories_table.c.id])),
 })

 c = Category()
 c.subcategories.append(Category()) # works great
 c._parent.append(Category()) # fails, c._parent is NoneType???

 Why isn't _parent a list? This is actually a one-to-many so there is
 only one parent, but assigning doesn't work either:

the relation from Category to _parent is many-to-one, so its a scalar  
in that direction (a one-to-many is always many-to-one in the reverse  
direction, and vice versa)


 c._parent = Category()

 Traceback (most recent call last):
   File C:\Program
 Files\Python\lib\site-packages\sqlalchemy-0.4.0beta5-py2.5.egg 
 \sqlalchemy\orm\attributes.py,
 line 76, in __set__
   File C:\Program
 Files\Python\lib\site-packages\sqlalchemy-0.4.0beta5-py2.5.egg 
 \sqlalchemy\orm\attributes.py,
 line 364, in set
   File C:\Program
 Files\Python\lib\site-packages\sqlalchemy-0.4.0beta5-py2.5.egg 
 \sqlalchemy\orm\attributes.py,
 line 300, in fire_replace_event
   File C:\Program
 Files\Python\lib\site-packages\sqlalchemy-0.4.0beta5-py2.5.egg 
 \sqlalchemy\orm\attributes.py,
 line 130, in sethasparent
 AttributeError: 'list' object has no attribute '_state'

I cant reproduce this, although the error to me seems like you are  
actually saying c._parent = [] (some list object).  If thats not it,  
send along a reproducing test script.


 I want to be able to create the tree of Category() objects from the
 top down and set relations via _parent, but how can I do this?

just the way you are doing it, c._parent = Category().  works for me  
on this end...



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