id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
25129	Migration crash on ForeignKey with a callable default that returns a model instance	Tim Graham	nobody	"For example, this model in Django's test suite (from `tests/delete/models.py`):
{{{#!python
class R(models.Model):
    is_default = models.BooleanField(default=False)

def get_default_r():
    return R.objects.get_or_create(is_default=True)[0]

class A(models.Model):
    setdefault = models.ForeignKey(R, default=get_default_r)
}}}
will fail like this:
{{{
  File ""/home/tim/code/django/django/db/migrations/migration.py"", line 123, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File ""/home/tim/code/django/django/db/migrations/operations/fields.py"", line 62, in database_forwards
    field,
  File ""/home/tim/code/django/django/db/backends/sqlite3/schema.py"", line 224, in add_field
    self._remake_table(model, create_fields=[field])
  File ""/home/tim/code/django/django/db/backends/sqlite3/schema.py"", line 104, in _remake_table
    self.effective_default(field)
  File ""/home/tim/code/django/django/db/backends/base/schema.py"", line 214, in effective_default
    default = field.get_db_prep_save(default, self.connection)
  File ""/home/tim/code/django/django/db/models/fields/related.py"", line 2017, in get_db_prep_save
    return self.target_field.get_db_prep_save(value, connection=connection)
  File ""/home/tim/code/django/django/db/models/fields/__init__.py"", line 721, in get_db_prep_save
    prepared=False)
  File ""/home/tim/code/django/django/db/models/fields/__init__.py"", line 969, in get_db_prep_value
    value = self.get_prep_value(value)
  File ""/home/tim/code/django/django/db/models/fields/__init__.py"", line 977, in get_prep_value
    return int(value)
TypeError: int() argument must be a string or a number, not 'R'
}}}
The issue is that [https://github.com/django/django/blob/c52822e7501e8478abf99465d8c9f3102dde618a/django/db/models/fields/related.py#L2003-L2008 ForeignKey.get_default()] doesn't return the model instance's ID because `self.remote_field.model` is `<class '__fake__.R'>` when migrating while the default function returns a ""real"" model instance."	Bug	closed	Migrations	1.8	Normal	fixed			Accepted	1	0	0	0	0	0