Hi,
I have a parent/superclass object in a polymorphic relationship which
is mapped against a select. The select is a table and a coalesce
function (the coalesce is to make up for the fact that the
polymorphic_on column doesn't exist).
All seems to be working fine on update, create etc but delete is
coming a cropper here:
/sqlalchemy/orm/mapper.pyc in _delete_obj(self, states,
uowtransaction)
1459 mapper = table_to_mapper[table]
1460 clause = sql.and_()
-> 1461 for col in mapper._pks_by_table[table]:
1462 clause.clauses.append(col == sql.bindparam
(col.key, type_=col.type))
1463 if mapper.version_id_col and
table.c.contains_column(mapper.version_id_col):
KeyError: Table('map_table', MetaData
(<sqlalchemy.engine.base.Connection object at 0x8751210>), Column
(...), ....)
In this instance map_table (names changed to protect the guilty) is
our child table and I've just done:
In [32]: q = ses.query(ChildClass)
In [33]: h = q[0]
In [34]: ses.delete(h)
In [35]: ses.flush()
At which point "kaboom".
Interestingly the 'mapper' in question in the traceback is the mapper
for a different child class i.e. NOT ChildClass in the ipython
example above, but 'table' is the the table mapped to ChildClass.
There are three of these child tables, all configured the same way and
one of them actually works for deleting. The one type of child class
that I can delete also belongs mapper in question when I get the above
traceback when trying to delete instances of the other two children. I
don't know if that's significant or not?
The only columns in the map_table are a foreign key to the parent
table / superclass and a foreign key to a related object (which are a
composite primary key) and an additional column.
I'm pretty sure that I'm doing something nasty, but the only really
out of the ordinary thing (as compared with the documentation) is that
the super class is mapped to something like:
my_super_table = select([superclass_table, func.coalesce
(<some_stuff>)]).alias('my_superclass_table')
This is the gist of the SQL that
>>> print select(my_super_table)
gives:
SELECT my_super_table.col1 ...
FROM
(SELECT h.col1 ...,
coalesce(
(SELECT 'C' FROM child1_map
WHERE child1_map.holiday_id = h.holiday_id),
(SELECT 'E' FROM dots.child2_map
WHERE child2_map.holiday_id = h.holiday_id),
(SELECT 'I' FROM child3_map
WHERE child1_map.holiday_id = h.holiday_id)
) AS my_polymorphic_column
FROM the_old_table h) my_super_table
This is the sql I want, and as I mentioned update and select seems to
be fine
So, is this a problem with incorrectly configuring cascade rules, or
have I found a corner case that should work but doesn't..?
Cheers,
Ben
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