Registering Models for Translation

Modeltranslation can translate model fields of any model class. For each model to translate a translation option class containing the fields to translate is registered with a special object called the translator.

Registering models and their fields for translation requires the following steps:

  1. Create a translation.py in your app directory.
  2. Create a translation option class for every model to translate.
  3. Register the model and the translation option class at modeltranslation.translator.translator.

The modeltranslation application reads the translation.py file in your app directory thereby triggering the registration of the translation options found in the file.

A translation option is a class that declares which fields of a model to translate. The class must derive from modeltranslation.translator.TranslationOptions and it must provide a fields attribute storing the list of fieldnames. The option class must be registered with the modeltranslation.translator.translator instance.

To illustrate this let’s have a look at a simple example using a News model. The news in this example only contains a title and a text field. Instead of a news, this could be any Django model class:

class News(models.Model):
    title = models.CharField(max_length=255)
    text = models.TextField()

In order to tell modeltranslation to translate the title and text fields, create a translation.py file in your news app directory and add the following:

from modeltranslation.translator import translator, TranslationOptions
from news.models import News

class NewsTranslationOptions(TranslationOptions):
    fields = ('title', 'text',)

translator.register(News, NewsTranslationOptions)

Note that this does not require to change the News model in any way, it’s only imported. The NewsTranslationOptions derives from TranslationOptions and provides the fields attribute. Finally the model and its translation options are registered at the translator object.

New in version 0.10.

If you prefer, register is also available as a decorator, much like the one Django introduced for its admin in version 1.7. Usage is similar to the standard register, just provide arguments as you normally would, except the options class which will be the decorated one:

from modeltranslation.translator import register, TranslationOptions
from news.models import News

@register(News)
class NewsTranslationOptions(TranslationOptions):
    fields = ('title', 'text',)

At this point you are mostly done and the model classes registered for translation will have been added some auto-magical fields. The next section explains how things are working under the hood.

TranslationOptions fields inheritance

New in version 0.5.

A subclass of any TranslationOptions will inherit fields from its bases (similar to the way Django models inherit fields, but with a different syntax).

from modeltranslation.translator import translator, TranslationOptions
from news.models import News, NewsWithImage

class NewsTranslationOptions(TranslationOptions):
    fields = ('title', 'text',)

class NewsWithImageTranslationOptions(NewsTranslationOptions):
    fields = ('image',)

translator.register(News, NewsTranslationOptions)
translator.register(NewsWithImage, NewsWithImageTranslationOptions)

The above example adds the fields title and text from the NewsTranslationOptions class to NewsWithImageTranslationOptions, or to say it in code:

assert NewsWithImageTranslationOptions.fields == ('title', 'text', 'image')

Of course multiple inheritance and inheritance chains (A > B > C) also work as expected.

Note

When upgrading from a previous modeltranslation version (<0.5), please review your TranslationOptions classes and see if introducing fields inheritance broke the project (if you had always subclassed TranslationOptions only, there is no risk).

Changes Automatically Applied to the Model Class

After registering the News model for translation a SQL dump of the news app will look like this:

$ ./manage.py sqlall news
BEGIN;
CREATE TABLE `news_news` (
    `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
    `title` varchar(255) NOT NULL,
    `title_de` varchar(255) NULL,
    `title_en` varchar(255) NULL,
    `text` longtext NULL,
    `text_de` longtext NULL,
    `text_en` longtext NULL,
)
;
CREATE INDEX `news_news_page_id` ON `news_news` (`page_id`);
COMMIT;

Note the title_de, title_en, text_de and text_en fields which are not declared in the original News model class but rather have been added by the modeltranslation app. These are called translation fields. There will be one for every language in your project’s settings.py.

The name of these additional fields is build using the original name of the translated field and appending one of the language identifiers found in the settings.LANGUAGES.

As these fields are added to the registered model class as fully valid Django model fields, they will appear in the db schema for the model although it has not been specified on the model explicitly.

Precautions regarding registration approach

Be aware that registration approach (as opposed to base-class approach) to models translation has a few caveats, though (despite many pros).

First important thing to note is the fact that translatable models are being patched - that means their fields list is not final until the modeltranslation code executes. In normal circumstances it shouldn’t affect anything - as long as models.py contain only models’ related code.

For example: consider a project where a ModelForm is declared in models.py just after its model. When the file is executed, the form gets prepared - but it will be frozen with old fields list (without translation fields). That’s because the ModelForm will be created before modeltranslation would add new fields to the model (ModelForm gather fields info at class creation time, not instantiation time). Proper solution is to define the form in forms.py, which wouldn’t be imported alongside with models.py (and rather imported from views file or urlconf).

Generally, for seamless integration with modeltranslation (and as sensible design anyway), the models.py should contain only bare models and model related logic.

Committing fields to database

If you are starting a fresh project and have considered your translation needs in the beginning then simply sync your database (./manage.py syncdb or ./manage.py schemamigration myapp --initial if using South) and you are ready to use the translated models.

In case you are translating an existing project and your models have already been synced to the database you will need to alter the tables in your database and add these additional translation fields. If you are using South, you’re done: simply create a new migration (South will detect newly added translation fields) and apply it. If not, you can use a little helper: The sync_translation_fields Command which can execute schema-ALTERing SQL to add new fields. Use either of these two solutions, not both.

If you are adding translation fields to a third-party app that is using South, things get more complicated. In order to be able to update the app in the future, and to feel comfortable, you should use the sync_translation_fields command. Although it’s possible to introduce new fields in a migration, it’s nasty and involves copying migration files, using SOUTH_MIGRATION_MODULES setting, and passing --delete-ghost-migrations flag, so we don’t recommend it. Invoking sync_translation_fields is plain easier.

Note that all added fields are by default declared blank=True and null=True no matter if the original field is required or not. In other words - all translations are optional, unless an explicit option is provided - see Required fields.

To populate the default translation fields added by modeltranslation with values from existing database fields, you can use the update_translation_fields command. See The update_translation_fields Command for more info on this.

Migrations (Django 1.7)

New in version 0.8.

Modeltranslation supports the migration system introduced by Django 1.7. Besides the normal workflow as described in Django’s Migration docs, you should do a migration whenever one of the following changes have been made to your project:

  • Added or removed a language through settings.LANGUAGES or settings.MODELTRANSLATION LANGUAGES.
  • Registered or unregistered a field through TranslationOptions.fields.

It doesn’t matter if you are starting a fresh project or change an existing one, it’s always:

  1. python manage.py makemigrations to create a new migration with the added or removed fields.
  2. python manage.py migrate to apply the changes.

Note

Support for migrations is implemented through fields.TranslationField.deconstruct(self) and respects changes to the null option.

Required fields

New in version 0.8.

By default, all translation fields are optional (not required). This can be changed using a special attribute on TranslationOptions:

class NewsTranslationOptions(TranslationOptions):
    fields = ('title', 'text',)
    required_languages = ('en', 'de')

It’s quite self-explanatory: for German and English, all translation fields are required. For other languages - optional.

A more fine-grained control is available:

class NewsTranslationOptions(TranslationOptions):
    fields = ('title', 'text',)
    required_languages = {'de': ('title', 'text'), 'default': ('title',)}

For German, all fields (both title and text) are required; for all other languages - only title is required. The 'default' is optional.

Note

Requirement is enforced by blank=False. Please remember that it will trigger validation only in modelforms and admin (as always in Django). Manual model validation can be performed via the full_clean() model method.

The required fields are still null=True, though.

TranslationOptions attributes reference

Quick cheatsheet with links to proper docs sections and examples showing expected syntax.

Classes inheriting from TranslationOptions can have following attributes defined:

TranslationOptions.fields(required)

List of translatable model fields. See Registering Models for Translation.

Some fields can be implicitly added through inheritance, see TranslationOptions fields inheritance.

TranslationOptions.fallback_languages

Control order of languages for fallback purposes. See Fallback languages.

fallback_languages = {'default': ('en', 'de', 'fr'), 'uk': ('ru',)}
TranslationOptions.fallback_values

Set the value that should be used if no fallback language yielded a value. See Fallback values.

fallback_values = _('-- sorry, no translation provided --')
fallback_values = {'title': _('Object not translated'), 'text': '---'}
TranslationOptions.fallback_undefined

Set what value should be considered “no value”. See Fallback undefined.

fallback_undefined = None
fallback_undefined = {'title': 'no title', 'text': None}
TranslationOptions.empty_values

Override the value that should be saved in forms on empty fields. See Formfields and nullability.

empty_values = ''
empty_values = {'title': '', 'slug': None, 'desc': 'both'}
TranslationOptions.required_languages

Control which translation fields are required. See Required fields.

required_languages = ('en', 'de')
required_languages = {'de': ('title','text'), 'default': ('title',)}

Supported Fields Matrix

While the main purpose of modeltranslation is to translate text-like fields, translating other fields can be useful in several situations. The table lists all model fields available in Django and gives an overview about their current support status:

Model Field 0.4 0.5 0.7
AutoField No No No
BigIntegerField No Yes* Yes*
BooleanField No Yes Yes
CharField Yes Yes Yes
CommaSeparatedIntegerField No Yes Yes
DateField No Yes Yes
DateTimeField No Yes Yes
DecimalField No Yes Yes
EmailField Yes* Yes* Yes*
FileField Yes Yes Yes
FilePathField Yes* Yes* Yes*
FloatField No Yes Yes
ImageField Yes Yes Yes
IntegerField No Yes Yes
IPAddressField No Yes Yes
GenericIPAddressField No Yes Yes
NullBooleanField No Yes Yes
PositiveIntegerField No Yes* Yes*
PositiveSmallIntegerField No Yes* Yes*
SlugField Yes* Yes* Yes*
SmallIntegerField No Yes* Yes*
TextField Yes Yes Yes
TimeField No Yes Yes
URLField Yes* Yes* Yes*
ForeignKey No No Yes
OneToOneField No No Yes
ManyToManyField No No No

* Implicitly supported (as subclass of a supported field)