I think I've tracked down the problem. Here is a bit of code from
django.db.models.fields.related.py:
def get_db_prep_lookup(self, lookup_type, value):
# If we are doing a lookup on a Related Field, we must be
# comparing object instances. The value should be the PK of
value,
# not value itself.
def pk_trace(value):
# Value may be a primary key, or an object held in a
relation.
# If it is an object, then we need to get the primary key
value for
# that object. In certain conditions (especially one-to-
one relations),
# the primary key may itself be an object - so we need to
keep drilling
# down until we hit a value that can be used for a
comparison.
v, field = value, None
try:
while True:
v, field = getattr(v, v._meta.pk.name), v._meta.pk
except AttributeError:
pass
if field:
if lookup_type in ('range', 'in'):
v = [v]
v = field.get_db_prep_lookup(lookup_type, v)
if isinstance(v, list):
v = v[0]
# BEGIN (got)
else:
field = self.rel.get_related_field()
if field:
v = field.get_db_prep_lookup(lookup_type, v)
# END (got)
return v
I added the part between BEGIN and END.
The problem was that, for the child model in multi-table inheritance,
its primary key in the database was being created by django as a
OneToOneField (which is correct, of course), and it was creating the
column using the proper type and everything, but you can see that
without the little part that I added, the value was not being properly
prepared for a lookup.
--gordy
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