Django: Access Primary Key In Models.filefield(upload_to) Location

I'd like to save my files using the primary key of the entry. Here is my code: def get_nzb_filename(instance, filename): if not instance.pk: instance.save() # Does not

Solution 1:

It seems you'll need to pre-generate your File models with empty file fields first. Then pick up one and save it with the given file object.

You can have a custom manager method like this;

defcreate_with_pk(self):
    instance = self.create()
    instance.save()     # probably this line is unneededreturn instance

But this will be troublesome if either of your fields is required. Because you are initially creating a null object, you can't enforce required fields on the model level.

EDIT

create_with_pk is supposed to be a custom manager method, in your code it is just a regular method. Hence self is meaningless. It is all properly documented with examples.

Solution 2:

You can do this by setting upload_to to a temporary location and by creating a custom save method.

The save method should call super first, to generate the primary key (this will save the file to the temporary location). Then you can rename the file using the primary key and move it to it's proper location. Call super one more time to save the changes and you are good to go! This worked well for me when I came across this exact issue.

For example:

classFile( models.Model ):
    nzb = models.FileField( upload_to='temp' )

    defsave( self, *args, **kwargs ):
        # Call save first, to create a primary keysuper( File, self ).save( *args, **kwargs )

        nzb = self.nzb
        if nzb:
            # Create new filename, using primary key and file extension
            oldfile = self.nzb.name
            dot = oldfile.rfind( '.' )
            newfile = str( self.pk ) + oldfile[dot:]

            # Create new file and remove old oneif newfile != oldfile:
                self.nzb.storage.delete( newfile )
                self.nzb.storage.save( newfile, nzb )
                self.nzb.name = newfile 
                self.nzb.close()
                self.nzb.storage.delete( oldfile )

        # Save again to keep changessuper( File, self ).save( *args, **kwargs )

Solution 3:

Context

Had the same issue. Solved it attributing an id to the current object by saving the object first.

Method

1. create a custom upload_to function
2. detect if object has pk
3. if not, save instance first, retrieve the pk and assign it to the object
4. generate your path with that

Sample working code :

classImage(models.Model):
    defupload_path(self, filename):
        ifnot self.pk:
            i = Image.objects.create()
            self.id = self.pk = i.idreturn"my/path/%s" % str(self.id)
    file = models.ImageField(upload_to=upload_path)

Solution 4:

You can create pre_save and post_save signals. Actual file saving will be in post_save, when pk is already created. Do not forget to include signals in app.py so they work. Here is an example:

_UNSAVED_FILE_FIELD = 'unsaved_file'@receiver(pre_save, sender=File)defskip_saving_file_field(sender, instance: File, **kwargs):
    ifnot instance.pk andnothasattr(instance, _UNSAVED_FILE_FIELD):
        setattr(instance, _UNSAVED_FILE_FIELD, instance.image)
        instance.nzb = None@receiver(post_save, sender=File)defsave_file_field(sender, instance: Icon, created, **kwargs):
    if created andhasattr(instance, _UNSAVED_FILE_FIELD):
        instance.nzb = getattr(instance, _UNSAVED_FILE_FIELD)
        instance.save()

Solution 5:

Here are 2 possible solutions:

Retrieve id before inserting a row

For simplicity I use postgresql db, although it is possible to adjust implementation for your db backend.

By default django creates id as bigserial (or serial depending on DEFAULT_AUTO_FIELD). For example, this model:

classFile(models.Model):
    nzb = models.FileField(upload_to=get_nzb_filename)
    name = models.CharField(max_length=256)

Produces the following DDL:

CREATETABLE "example_file" ("id" bigserial NOTNULLPRIMARY KEY, "nzb" varchar(100) NOTNULL, "name" varchar(256) NOTNULL);

There is no explicit sequence specification. By default bigserial creates sequence name in the form of tablename_colname_seq (example_file_id_seq in our case)

The solution is to retrieve this id using nextval :

def get_nextval(model, using=None):
    seq_name = f"{model._meta.db_table}_id_seq"
    if usingisNone:
        using= "default"
    with connections[using].cursor() ascursor:
        cursor.execute("select nextval(%s)", [seq_name])
        return cursor.fetchone()[0]

And set it before saving the model:

classFile(models.Model):
    # fields definitiondefsave(
        self, force_insert=False, force_update=False, using=None, update_fields=None):
        ifnot self.pk:
            self.pk = get_nextval(self, using=using)
            force_insert = Truesuper().save(
            force_insert=force_insert,
            force_update=force_update,
            using=using,
            update_fields=update_fields,
        )

Note that we rely on force_insert behavior, so make sure to read documentation and cover your code with tests:

from django.core.files.uploadedfile import SimpleUploadedFile
from django.forms import ModelForm
from django.test import TestCase

from example import models


classFileForm(ModelForm):
    classMeta:
        model = models.File
        fields = (
            "nzb",
            "name",
        )


classFileTest(TestCase):
    deftest(self):
        form = FileForm(
            {
                "name": "picture",
            },
            {
                "nzb": SimpleUploadedFile("filename", b"content"),
            },
        )
        self.assertTrue(form.is_valid())
        form.save()

        self.assertEqual(models.File.objects.count(), 1)
        f = models.File.objects.first()
        self.assertRegexpMatches(f.nzb.name, rf"files/{f.pk}_picture(.*)\.nzb")

---

Insert without nzt then update with actual nzt value

The idea is self-explanatory - we basically pop nzt on the object creation and save object again after we know id:

defsave(
    self, force_insert=False, force_update=False, using=None, update_fields=None):
    nzb = Noneifnot self.pk:
        nzb = self.nzb
        self.nzb = Nonesuper().save(
        force_insert=force_insert,
        force_update=force_update,
        using=using,
        update_fields=update_fields,
    )

    if nzb:
        self.nzb = nzb
        super().save(
            force_insert=False,
            force_update=True,
            using=using,
            update_fields=["nzb"],
        )

Test is updated to check actual queries:

def test(self):
    form = FileForm(
        {
            "name": "picture",
        },
        {
            "nzb": SimpleUploadedFile("filename", b"content"),
        },
    )
    self.assertTrue(form.is_valid())
    with CaptureQueriesContext(connection) as ctx:
        form.save()

    self.assertEqual(models.File.objects.count(), 1)
    f = models.File.objects.first()
    self.assertRegexpMatches(f.nzb.name, rf"files/{f.pk}_picture(.*)\.nzb")

    self.assertEqual(len(ctx.captured_queries), 2)
    insert, update = ctx.captured_queries
    self.assertEqual(
        insert["sql"],
        '''INSERT INTO "example_file" ("nzb", "name") VALUES ('', 'picture') RETURNING "example_file"."id"''',
    )
    self.assertRegexpMatches(
        update["sql"],
        rf"""UPDATE "example_file" SET "nzb" = 'files/{f.pk}_picture(.*)\.nzb' WHERE "example_file"."id" = {f.pk}""",
    )