Processing file uploads before object is saved

Question

I\'ve got a model like this:

class Talk(BaseModel):
  title        = models.CharField(max_length=200)
  mp3          = models.FileField(upload_to = u\'talks/         


        

Answer 1

You can access the file data in request.FILES while in your view.

I think that best way is to bind uploaded files to a form, override the forms clean method, get the UploadedFile object from cleaned_data, validate it anyway you like, then override the save method and populate your models instance with information about the file and then save it.

Answer 2

You could follow the technique used by ImageField where it validates the file header and then seeks back to the start of the file.

class ImageField(FileField):
    # ...    
    def to_python(self, data):
        f = super(ImageField, self).to_python(data)
        # ...
        # We need to get a file object for Pillow. We might have a path or we might
        # have to read the data into memory.
        if hasattr(data, 'temporary_file_path'):
            file = data.temporary_file_path()
        else:
            if hasattr(data, 'read'):
                file = BytesIO(data.read())
            else:
                file = BytesIO(data['content'])

        try:
            # ...
        except Exception:
            # Pillow doesn't recognize it as an image.
            six.reraise(ValidationError, ValidationError(
                self.error_messages['invalid_image'],
                code='invalid_image',
            ), sys.exc_info()[2])
        if hasattr(f, 'seek') and callable(f.seek):
            f.seek(0)
        return f

Answer 3

a cleaner way to get the file before be saved is like this:

from django.core.exceptions import ValidationError

#this go in your class Model
def clean(self):
    try:
        f = self.mp3.file #the file in Memory
    except ValueError:
        raise ValidationError("A File is needed")
    f.__class__ #this prints <class 'django.core.files.uploadedfile.InMemoryUploadedFile'>
    processfile(f)

and if we need a path, ther answer is in this other question