Custom model field: field.db_type not called for (initial) migration / docs wrong? (DurationField)

[Daniel Hahler]

While trying to use the ​DurationField with Django 1.7 I have noticed that the field is silently ignored from being added to the database.

While the initial migration is correct, the lookup for the db field type fails.

The ​docs state:

The db_type() method is called by Django when the framework constructs the CREATE TABLE statements for your application – that is, when you first create your tables.

This does not appear to be the case with migrations however, which only call field.db_parameters:

…/django-master/django/db/migrations/executor.py(60)migrate()

58 for migration, backwards in plan:
59 if not backwards:

---> 60 self.apply_migration(migration, fake=fake)

61 else:
62 self.unapply_migration(migration, fake=fake)

…/django-master/django/db/migrations/executor.py(95)apply_migration()

93 import ipdb; ipdb.set_trace()
94 project_state = self.loader.graph.project_state((migration.app_label, migration.name), at_end=False)

---> 95 migration.apply(project_state, schema_editor)

96 # For replacement migrations, record individual statuses
97 if migration.replaces:

…/django-master/django/db/migrations/migration.py(97)apply()

95 operation.state_forwards(self.app_label, new_state)
96 # Run the operation

---> 97 operation.database_forwards(self.app_label, schema_editor, project_state, new_state)

98 # Switch states
99 project_state = new_state

…/django-master/django/db/migrations/operations/models.py(28)database_forwards()

26 model = apps.get_model(app_label, self.name)
27 if router.allow_migrate(schema_editor.connection.alias, model):

---> 28 schema_editor.create_model(model)

29
30 def database_backwards(self, app_label, schema_editor, from_state, to_state):

…/django-master/django/db/backends/schema.py(191)create_model()

189 for field in model._meta.local_fields:
190 # SQL

--> 191 definition, extra_params = self.column_sql(model, field)

192 if definition is None:
193 continue

…/django-master/django/db/backends/schema.py(108)column_sql()

106 """
107 # Get the column's type and use that as the basis of the SQL

--> 108 db_params = field.db_parameters(connection=self.connection)

109 sql = db_paramstype
110 params = []

From the initial migration:

('runtime', durationfield.db.models.fields.duration.DurationField(help_text=u'Format: HH:MM:SS', null=True, verbose_name=u'Playtime')),

Commit ​e5983af (from 2012) changed BaseDatabaseSchemaEditor from using db_type to db_parameters.

(In commit ​1a9f13d the documentation got improved somehow, but appears to still reflect not the new/different behavior using migrations).

I have filed an ​issue for django-durationfield.

The source for the custom model field: ​duration.py.

Let me know if I should provide a simple test case / test app.

While at it, I think that there should have been a warning or assertion being triggered in this case. I have seen that the code considers this case to be a m2m field (or something similar), but those might look different at that point - and an assertion could be made there.

[Shai Berger]

This seems related to #22001.

[Daniel Hahler]

The commit introducing db_parameters (mentioned above, but linked incorrectly) is ​https://github.com/django/django/commit/ca9c3cd.

[Daniel Hahler]

Pull request at: ​https://github.com/django/django/pull/2425.

[Daniel Hahler]

The fix for this is now in the pull request for #22001.

[Marc Tamlyn <marc.tamlyn@…>]

In d22b291890c1736a40c0ad97448c7318df2eebb2:

Fixed #22001 -- Ensure db_type is respected.

db_parameters should respect an already existing db_type method and
return that as its type string. In particular, this was causing some
fields from gis to not be generated.

Thanks to @bigsassy and @blueyed for their work on the patch.

Also fixed #22260