django-translated-fields 0.5.0

Model translation for Django without magic-inflicted pain

Django model translation without magic-inflicted pain.

Installation and usage

After installing django-translated-fields in your Python environment all you have to do is define LANGUAGES in your settings and add translated fields to your models:

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

from translated_fields import TranslatedField

class Question(models.Model):
    question = TranslatedField(
        models.CharField(_('question'), max_length=200),
    )
    answer = TranslatedField(
        models.CharField(_('answer'), max_length=200),
    )

    def __str__(self):
        return self.question

Basic usage

Model fields are automatically created from the field passed to TranslatedField, one field per language. For example, with LANGUAGES = [('en', 'English'), ('de', 'German'), ('fr', 'French')], the following list of fields would be created: question_en, question_de, question_fr, answer_en, answer_de, and answer_fr.

This implies that when changing LANGUAGES you’ll have to run makemigrations and migrate too.

No question or answer model field is actually created. The TranslatedField instance is a descriptor which by default acts as a property for the current language’s field:

from django.utils.translation import override

question = Question(
    question_en='How are you?',
    question_de='Wie geht es Dir?',
    question_fr='Ça va?',
)

with override('en'):
    assert question.question == 'How are you?'

with override('de'):
    assert question.question == 'Wie geht es Dir?'

with override('fr'):
    question.question = 'Comment vas-tu?'

assert question.question_fr == 'Comment vas-tu?'

Changing field attributes per language

It is sometimes useful to have slightly differing model fields per language, e.g. for making the primary language mandatory. This can be achieved by passing a dictionary with keyword arguments per language as the second positional argument to TranslatedField.

For example, if you add a language to LANGUAGES when a site is already running, it might be useful to make the new language non-mandatory to simplify editing already existing data through Django’s administration interface.

The following example adds blank=True to the spanish field:

from translated_fields import TranslatedField

class Question(models.Model):
    question = TranslatedField(
        models.CharField(_('question'), max_length=200),
        {'es': {'blank': True}},
    )

Overriding attribute access (defaults, fallbacks)

There are no default values or fallbacks, only a wrapped attribute access. The default attribute getter and setter functions simply return or set the field for the current language (as returned by django.utils.translation.get_language). Note that the default getter and setter do not check whether a language is activated at all, or whether the field even exists (which might be the case when overriding languages). This implies that the getter might raise an AttributeError and the setter might set an attribute on the model instance not related to a model field.

Both getters and setters can be overridden by specifying your own attrgetter and attrsetter functions. E.g. you may want to specify a fallback to the default language (and at the same time allow leaving other languages’ fields empty):

from django.conf import settings
from translated_fields import TranslatedField, to_attribute

def fallback_to_default(name):
    def getter(self):
        return getattr(
            self,
            to_attribute(name),
        ) or getattr(
            self,
            # First language acts as fallback:
            to_attribute(name, settings.LANGUAGES[0][0]),
        )
    return getter

class Question(models.Model):
    question = TranslatedField(
        models.CharField(_('question'), max_length=200, blank=True),
        {settings.LANGUAGES[0][0]: {'blank': False}},
        attrgetter=fallback_to_default,
    )

A custom attrsetter which always sets all fields follows (probably not very useful, but hopefully instructive):

def set_all_fields(name):
    def setter(self, value):
        for field in getattr(self.__class__, name).fields:
            setattr(self, field, value)
    return setter

TranslatedField instance API

The TranslatedField descriptor has a few useful attributes (sticking with the model and field from the examples above):

• Question.question.fields contains the names of all automatically generated fields, e.g. ['question_en', 'question_...', ...].

• Question.question.languages is the list of language codes.

• Question.question.short_description is set to the verbose_name of the base field, so that the translatable attribute can be nicely used e.g. in ModelAdmin.list_display.

Using a different set of languages

It is also possible to override the list of language codes used, for example if you want to translate a sub- or superset of settings.LANGUAGES. Combined with attrgetter and attrsetter there is nothing stopping you from using this field for a different kind of translations, not necessarily bound to django.utils.translation or even languages at all.

Translated attributes without model field creation

If model field creation is not desired, you may also use the translated_attributes class decorator. This only creates the attribute getter property:

from translated_fields import translated_attributes

@translated_attributes('attribute', 'anything', ...)
class Test(object):
    attribute_en = 'some value'
    attribute_de = 'some other value'

Model admin support

The TranslatedFieldAdmin class adds the respective language to the label of individual fields. Instead of three fields named “Question” you’ll get the fields “Question [en]”, “Question [de]” and “Question [fr]”. It intentionally offers no functionality except for modifying the label of fields:

from django.contrib import admin
from translated_fields import TranslatedFieldAdmin
from .models import Question

@admin.register(Question)
class QuestionAdmin(TranslatedFieldAdmin, admin.ModelAdmin):
    pass

# For inlines:
# class SomeInline(TranslatedFieldAdmin, admin.StackedInline):
#     ...

Other features

There is no support for automatically referencing the current language’s field in queries or automatically adding fields to admin fieldsets and whatnot. The code required for these features isn’t too hard to write, but it is hard to maintain down the road which contradicts my goal of writing low maintenance software. Still, feedback and pull requests are very welcome! Please run the style checks and test suite locally before submitting a pull request though – all that this requires is running tox.