Name error: Can not import [model name]

Question

I am trying to link the model Post to the model Topic via a foreign key. When I run the makemigrations command, it raises an import error, and says that the name 'Topic' is not defined. What could be the cause of this? It certainly seems to be defined. I've pretty much ruled out that it is not a problem within the db.

class Post(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True)        
    title = models.CharField(max_length=100)
    summary = models.TextField(blank=True, null=True)
    content = models.TextField()
    draft = models.BooleanField(default=False)
    details = models.CharField(blank=True, null=True, max_length=250)
    updated = models.DateTimeField(auto_now=True, auto_now_add=False)
    timestamp = models.DateTimeField(auto_now=False, auto_now_add=True)
    topic = models.ForeignKey(Topic, blank=True, null=True)
    thumbnail = models.ImageField(upload_to='media', blank=True, null=True)


    def get_absolute_url(self):
        return reverse('posts:detail', kwargs={'pk': self.pk})

    def __str__(self):
        return self.title


class Topic(models.Model):
    name = models.CharField(max_length=50)
    description = models.TextField()
    picture = models.ImageField(upload_to='media', blank=True, null=True)
    isperson = models.BooleanField(default=False)
    ispolicy = models.BooleanField(default=False)
    positive = models.BooleanField(default=True)
    percent = models.CharField(max_length=5)

    def __str__(self):
        return self.name

Any ideas? I don't see any problems in this code, and neither did my IDE, which recognized the model Topic

Answer 1

I am considering that you have indented your code for Post model properly in your file.

Solution : Try to define Topic above Post.

Answer 2

First, this

topic = models.ForeignKey(Topic, blank=True, null=True)

should be this

topic = models.ForeignKey('Topic', blank=True, null=True)

This way it tells django that you're setting a foreign key to a model, which isn't declared yet, but will be declared further in the code.

Second, you should properly indent your Post model and its methods:

class Post(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True)
    title = models.CharField(max_length=100)
    summary = models.TextField(blank=True, null=True)
    content = models.TextField()
    draft = models.BooleanField(default=False)
    details = models.CharField(blank=True, null=True, max_length=250)
    updated = models.DateTimeField(auto_now=True, auto_now_add=False)
    timestamp = models.DateTimeField(auto_now=False, auto_now_add=True)
    topic = models.ForeignKey('Topic', blank=True, null=True)
    thumbnail = models.ImageField(upload_to='media', blank=True, null=True)

    def get_absolute_url(self):
        return reverse('posts:detail', kwargs={'pk': self.pk})

    def __str__(self):
        return self.title

Because as you have it now, django doesn't understand that the unindented fields belong to the Post model.