# 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 .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.

Added 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

Added 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). When dealing with abstract base classes, this can be handy:

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

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

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

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

The above example adds the fields `title` and `text` from the `AbstractNewsTranslationOptions` 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.

However, if the base class is not abstract, inheriting the `TranslationOptions` will cause errors, because the base `TranslationOptions` already took care of adding fields to the model. The example below illustrates how to add translation fields to a child model with a non-abstract base:

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

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

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

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

This will add the translated fields `title` and `text` to the `News` model and further add the translated field `image` to the `NewsWithImage` model.

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 names of these additional fields are built 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, 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 `MIGRATION_MODULES` setting, 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)

Added 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

Added 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.

Added in version 0.19.4.

To set required_languages for all models, use MODELTRANSLATION_REQUIRED_LANGUAGES setting, which accepts the same values as required_languages class variable.

## `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)