error when making migrations

Using Django Mystery Errors
1

I get the following errors when I run makemigrations “File “C:\Users\Casimir ABIRIYI\BlogAndTranslatorApp\blog\models.py”, line 24, in Post
attachments = models.ManyToManyField(Attachment, blank=True, related_name=‘attached_to_posts’)
^^^^^^^^^^
NameError: name ‘Attachment’ is not defined” Here are my modols.py file codes

from django.db import models
from django.utils.text import slugify
from django.contrib.auth.models import User
from django.urls import reverse
import logging

logger = logging.getLogger(__name__)

STATUS = ((0, 'Draft'), (1, 'Published'))
class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    date_created = models.DateTimeField(auto_now_add=True)
    slug = models.SlugField(max_length=200, unique=True)
    author = models.ForeignKey(User, on_delete=models.CASCADE, related_name='author_posts')
    status = models.IntegerField(choices=STATUS, default=1)
    owner = models.ForeignKey(User, on_delete=models.CASCADE, related_name='owner_posts')
    image = models.ImageField(upload_to='post_images/', null=True, blank=True)
    pdf = models.FileField(upload_to='post_pdfs/', blank=True, null=True)
    local_video = models.FileField(upload_to='post_local_videos/', blank=True, null=True)
    video_url = models.URLField(blank=True, null=True)
    audio = models.FileField(upload_to='post_audios/', blank=True, null=True)
    
    attachments = models.ManyToManyField(Attachment, blank=True, related_name='attached_to_posts')

    def get_absolute_url(self):
        return reverse('blog:post_detail', args=[str(self.slug)])
   
    def save(self, *args, **kwargs):
        if not self.slug:
            self.slug = slugify(self.title)
            logger.debug(f"Generated slug for post '{self.title}': {self.slug}")
        super().save(*args, **kwargs)
            
    def __str__(self):
        return self.title

    class Meta:
        ordering = ['-date_created']
        verbose_name = 'Post'
        verbose_name_plural = 'Posts'
        db_table = 'post_table'

class Attachment(models.Model):
    post = models.ForeignKey(Post, on_delete=models.CASCADE, related_name='attachments')
    file = models.FileField(upload_to='attachments/')
    
    def __str__(self):
        return self.file.name
2

Side note: When posting code here, enclose the code between lines of three backtick - ` characters. This means you’ll have a line of ```, then your code, then another line of ```. This forces the forum software to keep your code properly formatted. (I’ve taken the liberty of fixing your original post for you.)

There are two things I notice here.

First, models are defined in the order that they are defined in the file. At the point in time when Django is processing your Post model, the Attachment model in not yet defined.

From the docs for ForeignKey:

If you need to create a relationship on a model that has not yet been defined, you can use the name of the model, rather than the model object itself:

and it goes on to show how you do this by passing the name of the model as the first parameter instead of the class - in this case it would be:

The second item is more fundamental.

I notice you have a ManyToMany field associating Post with Attachment, and you also have a ForeignKey associating Attachment to Post. This seems redundant to me. If you have the ForeignKey associating Attachment with Post, I’m not seeing the need or value of the ManyToManyField. (Or the reverse - with the ManyToManyField, I don’t see any benefit to also having the ForeignKey.) I would recommend removing one or the other.

Or, if you do have a specific case where you need both, then I would move the ManyToManyField definition from Post to Attachment to make it clear that you have these duplicate references. (I’d also recommend having a substantial comment in that code to explain why you have both.)

3

Thank you so much, Mr. Ken. I have the ‘ManyToManyField’ and the ForeignKey’ fields, in the Post and attachment models, because I want Users to be able to attach multiple files to their posts

4

That explains the FK field - why then do you have a ManyToManyField?

5

Thank you so much, for your contributions. I really appreciate.