I think I found the problem: if the target object has a
prepare_database_save() field, which it did (because it was a Django
model object), this function will be called, replacing the target
object (in subqueries.py)
NOTE - "target object" means the value of the field for a model
instance, which will be converted by the get_db_prep_value function.
This is confusing behavior. The fix is to add a pre_save() function,
def get_db_prep_value(self, value):
if isinstance(value, (int, long)):
return value
assert isinstance(value.chainId, (int, long))
return value.chainId
# NOTE - avoid Django prepare_database_save() call on value
def pre_save(self, model, add):
return self.get_db_prep_value(getattr(model, self.attname))
On Sep 6, 3:21 pm, gatoatigrado <gatoatigr...@gmail.com> wrote:
> Hi all,
>
> I wrote a custom field which should get an object by a primary key
> value (chainId). The base storage type is an int. I have a call that
> does "obj.save(force_update=True)", and I get this "may not be NULL"
> error. I set a debug point in execute_sql(), and indeed, it seems to
> say "UPDATE ... fieldname = NULL, ... WHERE ...". My get_db_prep_value
> () looks like this:
>
> def get_db_prep_value(self, value):
> assert isinstance(value.chainId, (int, long))
> return value.chainId
>
> If anyone has encountered a similar problem, I'd appreciate it.
>
> regards,
> Nicholas
>
> class ImmutableRefField(models.Field):
> __metaclass__ = models.SubfieldBase
>
> def __init__(self, typegetter, *argv, **kwargs):
> self.typegetter = typegetter
> models.Field.__init__(self, *argv, **kwargs)
>
> def get_internal_type(self):
> return "IntegerField"
>
> def to_python(self, value):
> if isinstance(value, (int, long, str)):
> clstype = self.typegetter()
> assert issubclass(clstype, ImmutableModel)
> return clstype.ReferenceGetter(clstype, value)
> elif isinstance(value, (ImmutableModel,
> ImmutableModel.ReferenceGetter)):
> return value
> raise NotImplementedError, "unknown value type %r" %(value)
>
> # dynamically typed is nice; this could be a reference or an
> object
> def get_db_prep_value(self, value):
> assert isinstance(value.chainId, (int, long))
> return value.chainId
>
> def get_db_prep_lookup(self, lookup_type, value):
> if lookup_type == 'exact':
> return [self.get_db_prep_value(value)]
> pyhelp = help; import pdb; pdb.set_trace()
> if lookup_type == 'in':
> return [force_unicode(v) for v in value]
> if lookup_type == 'isnull':
> return []
> raise FieldError('Invalid lookup type: %r' % lookup_type)
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