<p>试着用引号将模型括起来:</p>
<pre><code>class SubCategory(models.Model):
name = models.CharField(max_length=100)
slug = models.SlugField(max_length=110)
description = models.TextField(default='')
ordering = models.PositiveIntegerField(default=1)
category = models.ForeignKey('Category')
created_on = models.DateTimeField(auto_now_add=True)
created_by = models.ForeignKey('User')
updated_on = models.DateTimeField(blank=True, null=True)
updated_by = models.ForeignKey('User', related_name='+')
num_topics = models.IntegerField(default=0)
num_posts = models.IntegerField(default=0)
last_topic = models.ForeignKey('Topic', related_name='+')
class Topic(models.Model):
name = models.CharField(max_length=300)
slug = models.SlugField(max_length=300)
description = models.TextField(default='')
subcategory = models.ForeignKey("SubCategory")
created_on = models.DateTimeField(auto_now_add=True)
created_by = models.ForeignKey('User')
updated_on = models.DateTimeField(blank=True, null=True)
updated_by = models.ForeignKey('User', related_name='+')
</code></pre>