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 `` 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