Django-parler unique_together constraint between translated and normal field

Question

I want to make unique_together constraint with django-parler between translated field and normal field.

I'd like to do this:

class Part(TranslatableModel):
    code = CharField('code')
    translations = TranslatedFields(
        name = CharField('name')
    )

    class Meta:
        constraints = [
            UniqueConstraint(
                fields=['code', 'name'],
                name='constraint_name',  
            )
        ]

but then I get error:

Traceback (most recent call last):
  File "manage.py", line 14, in <module>
    execute_from_command_line(sys.argv)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/core/management/base.py", line 323, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/core/management/base.py", line 364, in execute
    output = self.handle(*args, **options)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/core/management/base.py", line 83, in wrapped
    res = handle_func(*args, **kwargs)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/core/management/commands/migrate.py", line 234, in handle
    fake_initial=fake_initial,
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/migrations/executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/migrations/executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/migrations/executor.py", line 245, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/migrations/migration.py", line 124, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/migrations/operations/models.py", line 827, in database_forwards
    schema_editor.add_constraint(model, self.constraint)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/backends/sqlite3/schema.py", line 405, in add_constraint
    self._remake_table(model)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/backends/sqlite3/schema.py", line 279, in _remake_table
    self.create_model(new_model)
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/backends/base/schema.py", line 296, in create_model
    constraints = [constraint.constraint_sql(model, self) for constraint in model._meta.constraints]
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/backends/base/schema.py", line 296, in <listcomp>
    constraints = [constraint.constraint_sql(model, self) for constraint in model._meta.constraints]
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/models/constraints.py", line 89, in constraint_sql
    fields = [model._meta.get_field(field_name).column for field_name in self.fields]
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/models/constraints.py", line 89, in <listcomp>
    fields = [model._meta.get_field(field_name).column for field_name in self.fields]
  File "/home/lauri/työt/p/venv/lib/python3.6/site-packages/django/db/models/options.py", line 567, in get_field
    raise FieldDoesNotExist("%s has no field named '%s'" % (self.object_name, field_name))
django.core.exceptions.FieldDoesNotExist: NewPart has no field named 'name'

I'm not very aware of insides of django-parler so I'm not able to move forward with this.

Answer 1

When you make migrations there will be two tables Part and PartTranslation. What you want is single translation for single post. So the following lines solves your problem

    translations = TranslatedFields(
        name = CharField('name'),
        meta={'unique_together': [('name', 'language_code')]}
    )

For uniqueness of Parts just make the code field unique.

  code = CharField('code', unique=True)