Hi,
I'm trying to save space in database rows in tables that have bigint-sized
numbers of rows. One of the things I'm trying to do is using a smallint for
the `id` on one of the models that is pointed to from those big tables:
I have a model A with a custom AutoField for its primary key that uses a
smallint instead of int by way of a custom db_type method. I have a second
model B that subclasses A. Model C is the model with the large number of
rows and has a foreign key to B. Django generates an int-sized column in
model B for the foreign key to the superclass A. I hoped for a
smallint-sized column, as that's what the related field is using. MySQL
spits out an error.
I'm reading the ForeignKey.db_type method (rel 1.6): I don't quite
understand why it insists on returning the db_type from IntegerField when
my field is an instance of AutoField. I'm guessing it has something to do
with AutoField's db_type returning AUTO_INCREMENT along with its column
type. This works if the field is specifically of the builtin type
AutoField, but not necessarily with some random subclass;
And as I understand it from the __new__ in ModelBase I invariably end up
with a OneToOneField for the `a_ptr_id` field in the subclass. So I don't
seem to be able to "patch" that field, like I can with the `id` field in
model A or a regular foreign key.
All I can come up with is this yucky:
>>> B._meta.get_field('a_ptr').db_type = lambda connection: 'smallint'
..which works, or I could create a standalone model B that "inherits" from
model A without using Python inheritance, i.e. explicitly create a smallint
primary key and fiddle with create statements so that I also get records in
A.
Is there any (nice) way I can persuade Django to return a different db_type
for that OneToOneField in the subclass?
thanks,
Jeroen Pulles
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