How do I specify a null relation in SQLAlchemy?

Posted by Jesse on Stack Overflow See other posts from Stack Overflow or by Jesse
Published on 2010-05-19T08:06:21Z Indexed on 2010/05/19 8:10 UTC
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Filed under:

python

|

sqlalchemy

|

foreign-key-relationship

Not sure what the correct title for this question should be. I have the following schema:

Matters have a one-many relationship to WorkItems.
WorkItems have a one-one (or one-zero) relationship to LineItems.

I am trying to create the following relation between Matters and WorkItems

Matter.unbilled_work_items = orm.relation(WorkItem,
  primaryjoin = (Matter.id == WorkItem.matter_id) and (WorkItem.line_item_id == None),
  foreign_keys = [WorkItem.matter_id, WorkItem.line_item_id],
  viewonly=True
)

This throws:

AttributeError: '_Null' object has no attribute 'table'

That seems to be saying that the second clause in the primaryjoin returns an object of type _Null, but it seems to be expecting something with a "table" attribute.

This seems like it should be pretty straightforward to me, am I missing something obvious?

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