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:
- Create a translation.py in your app directory.
- Create a translation option class for every model to translate.
- Register the model and the translation option class at the 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 the modeltranslation app to translate the title and text field, 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.
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.
When upgrading from a previous modeltranslation version, 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.
If you are starting a fresh project and have considered your translation needs in the beginning then simply sync your database 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. Note that all added fields are declared blank=True and null=True no matter if the original field is required or not. In other words - all translations are optional. To populate the default translation fields added by the modeltranslation application you can use the update_translation_fields command below. See The update_translation_fields Command for more infos on this.
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:
* Implicitly supported (as subclass of a supported field)