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Model translation for Django without magic-inflicted pain

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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?",
)

# The default getter automatically returns the value
# in the current language:
with override("en"):
    assert question.question == "How are you?"

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

# The default setter can also be used to set the value
# in the current language:
with override("fr"):
    question.question = "Comment vas-tu?"

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

TranslatedField has a fields attribute that returns a list of all the language fields created.

assert Question.answer.fields == ["answer_en", "answer_de", "answer_fr"]

For more attributes look at the ``TranslatedField`` instance API section below.

question and answer can only be used with model instances, they do not exist in the database. If you want to use queryset methods which reference individual translated fields you have to use language-specific field names yourself. If you wanted to fetch only the english question and answer fields you could do this as follows:

questions = Question.objects.values_list("question_en", "answer_en")

Or better yet, using the to_attribute helper which automatically uses the active language (if you don’t pass a specific language code as its second argument):

from django.utils.translation import override
from translated_fields import to_attribute

with override("en"):
    questions = Question.objects.values_list(
        to_attribute("question"), to_attribute("answer")
    )

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). The default getter falls back to the first language of the field in case get_language() returns None. Apart from that the default getter has no safetyfeatures and may 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, field):
    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,
    )

Maybe you’re using locales with region codes such as fr-fr where you want to fall back to the language without a region code. An example attrgetter implementation follows:

from translated_fields import to_attribute

def fallback_to_all_regions(name, field):
    def getter(self):
        value = getattr(self, to_attribute(name), None)
        if value:
            return value
        return getattr(self, to_attribute(name, get_language().split("-")[0]))

    return getter

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

def set_all_fields(name, field):
    def setter(self, value):
        for field in field.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):
#     ...

As mentioned above, the fields attribute on the TranslatedField instance contains the list of generated fields. This may be useful if you want to customize various aspects of the ModelAdmin subclass. An example showing various techniques follows:

from django.contrib import admin
from django.utils.translation import gettext_lazy as _
from translated_fields import TranslatedFieldAdmin, to_attribute
from .models import Question

@admin.register(Question)
class QuestionAdmin(TranslatedFieldAdmin, admin.ModelAdmin):
    # Pack question and answer fields into their own fieldsets:
    fieldsets = [
        (_("question"), {"fields": Question.question.fields}),
        (_("answer"), {"fields": Question.answer.fields}),
    ]

    # Show all fields in the changelist:
    list_display = [
        *Question.question.fields,
        *Question.answer.fields
    ]

    # Order by current language's question field:
    def get_ordering(self, request):
        return [to_attribute("question")]

Note

It’s strongly recommended to set the verbose_name of fields when using TranslatedFieldAdmin, the first argument of most model fields. Otherwise, you’ll get duplicated languages, e.g. “Question en [en]”.

Forms

django-translated-fields provides a helper when you want form fields’ labels to contain the language code. If this sounds useful to you do this:

from django import forms
from translated_fields.utils import language_code_formfield_callback
from .models import Question

class QuestionForm(forms.ModelForm):
    formfield_callback = language_code_formfield_callback

    class Meta:
        model = Question
        fields = [
            *Question.question.fields,
            *Question.answer.fields
        ]

You may also globally configure language code labels to be shown within a block:

from translated_fields import show_language_code

def view(request):
    form = ...
    with show_language_code(True):
        return render(request, "...", {"form": form})

Please note that the response has to be rendered within the show_language_code block. This doesn’t happen automatically when using Django’s TemplateResponse objects.

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.

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