title: Django PostgreSQL DatabaseError: relation "categories" does not exist
body: <p>I am working on a Django app. Initially I was using MySQL for database. Then, I needed to deploy a demo app on heroku, which uses PostgreSQL.</p>
  
  <p>I am getting an error in heroku when I try to create an object, even from shell.</p>
  
  <p>This is what I am trying to do:</p>
  
  <pre><code>&gt;&gt; from store.models import Product, Category
  &gt;&gt; cat = Category()
  &gt;&gt; cat.name = 'books'
  &gt;&gt; cat.description = 'books'
  &gt;&gt; cat.slug = 'books'
  &gt;&gt; cat.save()
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>......
  DatabaseError: relation "categories" does not exist
  </code></pre>
  
  <p>Here's my Category and Product models</p>
  
  <pre><code>class Category(models.Model):
    name = models.CharField(max_length=50)
    description = models.TextField()
    slug = models.SlugField(max_length=50, unique=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
  
  class Product(models.Model):
    name = models.CharField(max_length=100, unique=True)
    description = models.TextField()
    price = models.DecimalField(max_digits=9, decimal_places=2)
    slug = models.SlugField(max_length=50, unique=True)
    categories = models.ManyToManyField(Category)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
  </code></pre>
  
  <p>It works very well with MySQL, but not with PostgreSQL.</p>
  
  <p>Can anyone help?</p>
  
  <p>Thanks.</p>