Django Generic Foreign keys - Good or Bad considering the SQL performance?

Add an index_together Meta option to your model:

class Meta:
    index_together = [('cprofile_id', 'cprofile_type')]

I'd like to quote some words from David Cramer: developer of Disqus, Django commiter

Generic relations are fine. They are not slow, just more difficult to manage in your code base.

I saw many people tell others don't use generic relations because it's slow, but never tell how it's slow.

Avoid Django's GenericForeignKey has a good and thorough description of the database design antipatterns involved in generic foreign keys (or "polymorphic associations," as they call them in rails-speak).

As for performance, it takes 3 database queries every time you want to retrieve the related GenericForeignKey resource from your model:

1. SELECT object_id_field, object_id from myapp_a WHERE id=1;
2. SELECT app_label, model FROM django_content_type WHERE id=A.object_type_field;
   • In application code, compute table name model + _ + app_label
3. SELECT A.object_id_field FROM TABLE_NAME;

When people say that Generic Foreign Keys have a performance penalty, they are referencing this query overhead.

There are only a very narrow set of circumstances under which you really want to use generic foreign keys. The above-linked article discusses those, as well.