django-linguist

django-linguist is a Django application for flexible model translations.

Here a few principles that define this application in comparaison to others applications:

Translations are stored in single one table and you can also use a different one per model
No "one i18n table per model", say "goodbye" to nightmares :)
No more painful migrations
Not tied to model class names, you are free to use your own identifiers
No ORM query hacks, it does not patch anything and it will be easier for you to upgrade your Django
No magic, it uses metaclasses and mixins and everything is explicit
Dead simple to plug in an existing project
Django admin ready

If you are looking for a "one-i18n-table-per-model" way, django-parler is an awesome alternative.

Installation

$ pip install django-linguist

In your settings.py, add linguist to INSTALLED_APPS:

INSTALLED_APPS = (
    # Your other apps here
    'linguist',
)

Then synchronize database:

# >= Django 1.7
$ python manage.py migrate linguist

# < Django 1.7
$ python manage.py syncdb

That's all.

Configuration

Models

In three steps:

Add linguist.metaclasses.ModelMeta to your model as metaclass
Add linguist.mixins.ManagerMixin to your model manager
Add linguist settings in your model's Meta

Don't worry, it's fairly simple:

from django.db import models
from django.utils.translation import gettext_lazy as _

from linguist.metaclasses import ModelMeta as LinguistMeta
from linguist.mixins import ManagerMixin as LinguistManagerMixin


class PostManager(LinguistManagerMixin, models.Manager):
    pass


class Post(models.Model, meta=LinguistMeta):
    title = models.CharField(max_length=255)
    body = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    objects = PostManager()

    class Meta:
        verbose_name = _('post')
        verbose_name_plural = _('posts')
        linguist = {
            'identifier': 'can-be-anything-you-want',
            'fields': ('title', 'body'),
            'default_language': 'fr',
        }

The linguist meta requires:

identifier: a unique identifier for your model (can be anything you want)
fields: list or tuple of model fields to translate

And optionally requires:

default_language: the default language to use
default_language_field: the field that contains the default language to use (see below)
decider: the translation model to use instead of the default one (see below)

That's all. You're ready.

Default language per instance

Sometimes, you need to define default language at instance level. Linguist supports this feature via the default_language_field option. Add a field in your model that will store the default language then simply give the field name to Linguist.

Let's take an example:

from django.db import models
from django.utils.translation import gettext_lazy as _

from linguist.metaclasses import ModelMeta as LinguistMeta
from linguist.mixins import ManagerMixin as LinguistManagerMixin


class PostManager(LinguistManagerMixin, models.Manager):
    pass


class Post(models.Model, meta=LinguistMeta):
    title = models.CharField(max_length=255)
    body = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    lang = models.CharField(max_length=5, default='en')
    objects = PostManager()

    class Meta:
        verbose_name = _('post')
        verbose_name_plural = _('posts')
        linguist = {
            'identifier': 'can-be-anything-you-want',
            'fields': ('title', 'body'),
            'default_language': 'en',
            'default_language_field': 'lang',
        }

Custom table for translations

By default, Linguist stores translations into linguist.models.Translation table. So in a single one table. If you need to use another table for a specific model, Linguist provides a way to override this behavior: use deciders.

That's really easy to implement.

You can do it in three steps:

Create a model that inherits from linguist.models.base.Translation
Don't forget to define it as concrete (abstract = False in Meta)
Give this model to Linguist meta decider option

This example will show you the light:

from django.db import models
from django.utils.translation import gettext_lazy as _

from linguist.metaclasses import ModelMeta as LinguistMeta
from linguist.mixins import ManagerMixin as LinguistManagerMixin
from linguist.models.base import Translation


# Our Post model decider
class PostTranslation(Translation):
    class Meta:
        abstract = False


class PostManager(LinguistManagerMixin, models.Manager):
    pass


class Post(models.Model, meta=LinguistMeta):
    title = models.CharField(max_length=255)
    body = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    objects = PostManager()

    class Meta:
        verbose_name = _('post')
        verbose_name_plural = _('posts')
        linguist = {
            'identifier': 'can-be-anything-you-want',
            'fields': ('title', 'body'),
            'default_language': 'fr',
            'decider': PostTranslation,
        }

django.contrib.admin

Simply use linguist.admin.TranslatableModelAdmin class:

from django.contrib import admin
from linguist.admin import TranslatableModelAdmin
from .models import Post


class PostAdmin(TranslatableModelAdmin):
    list_display = ('title', 'body', 'created_at')

admin.site.register(Post, PostAdmin)

Bonus! You can display instance's languages in list_display via the languages_column property provided by the admin class:

from django.contrib import admin
from linguist.admin import TranslatableModelAdmin
from .models import Post


class PostAdmin(TranslatableModelAdmin):
    list_display = ('title', 'body', 'languages_column', 'created_at')

admin.site.register(Post, PostAdmin)

How it works

Linguist adds virtual language fields to your models. For the example above, if we have en, fr and it in settings.LANGUAGES, it dynamically adds the following fields in Post model:

Post.title_en
Post.title_fr
Post.title_it
Post.body_en
Post.body_fr
Post.body_it

These fields are virtuals. They don't exist in Post table. There are wrappers around linguist.Translation model. All translations will be stored in this table.

When you set/get post.title, Linguist will use the current active language and will set/get the correct field for this language. For example, if your default language is English (en), then Post.title will refer to post.title_en.

The ModelMixin enhance your model with the following properties and methods:

instance.linguist_identifier (read-only property): Your model identifier defined in the related translation class. Shortcut pointing on instance._linguist.identifier.
instance.default_language (read-write property): The default language to use. Shortcut pointing on instance._linguist.default_language.
instance.translatable_fields (read-only property): Translatable fields defined in the related translation class. Shorcut pointing on instance._linguist.fields.
instance.available_languages (read-only property): Available languages for this instance (content translated in these languages).
instance.cached_translations_count (read-only property): Returns the number of cached translations. Each time you set a new language and set content on translatable fields, a cache is created for each language and field. It will be used to create Translation objets at instance saving.
instance.active_language(): Set the current active language for the instance.
instance.clear_translations_cache(): Remove all cached translations. Be aware, any content you set will be dropped. So no translation will be created/updated at saving.

# Let's create a new Post
>>> post = Post()

# Set English content
>>> post.activate_language('en')
>>> post.title = 'Hello'

# Now set French content
>>> post.activate_language('fr')
>>> post.title = 'Bonjour'

# Be sure everything works as expected for English
>>> post.activate_language('en')
>>> post.title
Hello

# And now for French
>>> post.activate_language('fr')
>>> post.title
Bonjour

# Sweet! Save translations!
>>> post.save()

Preloading

To improve performances, you can preload/prefetch translations.

For a queryset (your queryset must inherit from Linguist manager/queryset):

>>> Post.objects.with_translations()

For a list of objects (all your objects must inherit from Linguist model):

>>> from linguist.helpers import prefetch_translations
>>> posts = list(Post.objects.all())
>>> prefetch_translations(posts)

For an instance (it must inherit from Linguist model):

>>> post = Post.objects.first()
>>> post.prefetch_translations()

All translations will be cached in instances. Database won't be hit anymore.

This preloading system takes three parameters:

field_names: list of translatable field names to filter on
languages: list of languages to filter on
populate_missing: boolean if you want to populate cache for missing translations (defaults to True)
chunks_length: chunk limit for SELECT IN ids for translations

For example, we only want to prefetch post titles in English without populating missing translations with an empty string:

>>> Post.objects.with_translations(field_names=['title'], languages=['en'], populate_missing=False)

It works the same for:

QuerySet with_translations()
Helper prefetch_translations()
Instance method prefetch_translations()

What does "populating missing translations" mean?

Simple. By default, when you prefetch translations, instances cache will be populated with empty strings for all supported languages (see settings). For example, if you have en, fr and it as supported languages and only have English translations, if you try to access other languages, an empty string will be returned without any database hit:

>>> Post.objects.with_translations()
>>> post.title_fr # no database hit here because
''

Now, if you explicitly set populate_missing to False, if a translation is not found, it will be fetched from database.

>>> Post.objects.with_translations(populate_missing=False)
>>> post.title_fr # database hit here
''

Development

# Don't have pip?
$ sudo easy_install pip

# Don't already have virtualenv?
$ sudo pip install virtualenv

# Clone and install dependencies
$ git clone https://github.com/ulule/django-linguist.git
$ cd django-linguist
$ make devenv

# Enable virtual environment.
$ source .venv/bin/activate

# Launch tests
$ make test

# Launch example project
$ make serve

ulule/django-linguist

ulule

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