Django Rest Framework - Downloading files on server

I am writing an API that allows the client to post a link to a file, and then I want to download the file and store it as a FileField on one of my models. Here is the code I have so far:

Serializer:

from rest_framework import serializers
from django.core.files import File
from rest_framework.serializers import ValidationError

class MySerializer(serializers.ModelSerializer):

    class Meta:
        model = MyModel
        fields = ('url')

    def to_internal_value(self, data):
        validated = dict()

        url = data.get('url')

        # do url validation here

        # download the file to local disk

        validated['file'] = File(open('path/to/downloaded/file'))
        validated['url'] = url

        return validated 

Model:

from django.db import models


class MyModel(models.Model):
    url = models.CharField(max_length=255)
    file = models.FileField(upload_to='files/')

For the view, I use a generic ListCreateAPIView.

There are two main problems, first is that with my current implementation, I end up with two copies of the file because I download it to some location on disk first, and then later when the FileField is stored into the database it copies the file again to the files/ folder. Is there some way to avoid this? Secondly, how can I download the file asynchronously yet still be able to add the FileField attribute on the model after the download has completed?