How to get the fieldname of a FileField in the upload_to method, for a field translated with modeltranslation in Django?

Question

I am using django modeltranslation on a FileField.

I would like this file to be uploaded in a path /path/to/file/<lang>/file.ext and I guess the best way is to extract the lang from the fieldname (file_en, file_it, file_fr, ...) where upload_to is operating.

# models.py
def upload_method(instance, filename):
   lang = ""  # how to get this variable? 
   return f"/path/to/file/{lang}/file.ext"

class Obj(models.Model):
   file = models.FileField(upload_to=upload_method)

# translation.py
@register(models.Obj)
class ObjTranslationOptions(TranslationOptions):
    fields = ("file", )

Answer 1

Something like this should work.

from modeltranslation.translator import translator
from django.db.models import FileField
import os


class TranslationMeta(type):
    def __init__(self, name, bases, attrs):
        for attrname, attrvalue in attrs.items():
            if self.is_translated_field(name, attrname):
                field = attrvalue
                if isinstance(field, FileField):
                    self.update_upload_to(field, attrname)
        super().__init__(name, bases, attrs)

    def is_translated_field(self, class_name, attr_name):
        opts = translator.get_options_for_model(self)
        return attr_name in opts.get_field_names()

    def update_upload_to(self, field, attr_name):
        opts = translator.get_options_for_model(self)
        translated_fields = opts.fields[attr_name]
        for trans_field in translated_fields:
            # print(trans_field.name)
            # print(trans_field.language)
            trans_field.upload_to = self.custom_upload_to(field.upload_to, trans_field.language)    

    def custom_upload_to(self, base_upload_to, language):
        # If the original upload_to parameter is a callable,
        # return a function that calls the original upload_to
        # function and inserts the language as the final folder
        # in the path
        # If the original upload_to function returned /path/to/file.png,
        # then the final path will be /path/to/en/file.png for the
        # english field
        if callable(base_upload_to):
            def upload_to(instance, filename):
                path = base_upload_to(instance, filename)
                return os.path.join(
                    os.path.dirname(path),
                    language,
                    os.path.basename(path))
            return upload_to
        # If the original upload_to parameter is a path as a string,
        # insert the language as the final folder in the path
        # /path/to/file.png becomes /path/to/en/file.png for the
        # english field
        else:
            return os.path.join(
                os.path.dirname(base_upload_to),
                language,
                os.path.basename(base_upload_to))


# This is how you would use this class
class MyModel(models.Model, metaclass=TranslationMeta):
    field = FileField()

m = MyModel(models.Model)
print(m.field.upload_to)

It uses introspection to dynamically override the upload_to parameter of every language-specific FileField generated by django-modeltranslation behind the scenes.

With this model for instance:

class MyModel(models.Model):
    field = FileField(upload_to=...)

if you have defined field as a translatable field by adding

from modeltranslation.translator import register, TranslationOptions
from . import models

@register(models.MyModel)
class MyModelTranslationOptions(TranslationOptions):
    fields = ("field",)

in translation.py, django-modeltranslation will generate something like

class MyModel(models.Model):
    field = FileField(upload_to=...)
    field_en = FileField(upload_to=...)
    field_fr = FileField(upload_to=...)

if you have en and fr defined in your LANGUAGES settings.

If the upload_to parameter passed to the FileField was a path as a string, it is overridden with the same path in which a folder for the language is inserted. If it is a function, then the folder for the language is inserted in the path returned by this function.

For instance if you have

class MyModel(models.Model):
    field = FileField(upload_to="/path/to/file.png")

or

def get_upload_path(instance, filename):
    return "path/to/file.png"

class MyModel(models.Model):
    field = FileField(upload_to=get_upload_path)

then, in both cases:

• the English version of the file will be stored under /path/to/en/file.png
• the French version of the file will be stored under /path/to/fr/file.png

Answer 2

Try to use get_language method:

from django.utils.translation import get_language

def upload_method(instance, filename):
   lang = get_language()
   return f"/path/to/file/{lang}/file.ext"