title: Peewee throws KeyError: 'f'
body: <p>So I can't figure out what the error here is (I'm pretty sure I'm just doing something stupid). Any help would be appreciated.
  Here's models.py</p>
  
  <pre><code>DATABASE = SqliteDatabase('social.db')
  
  class User(UserMixin, Model):
      username = CharField(unique=True)
      email = CharField(unique=True)
      password = CharField(max_length=100)
      joined_at = DateTimeField(default=datetime.datetime.now)
      is_admin = BooleanField(default=False)
  
      class Meta:
          database = DATABASE
          order_by = ('-joined_at',)
  
  class Post(Model):
      timestamp = DateTimeField(default=datetime.datetime.now)
      user = ForeignKeyField(User, related_name='posts')
      content = TextField()
  
      class Meta:
          database = DATABASE
          order_by = ('-timestamp',)
  
  class Relationship(Model):
      from_user = ForeignKeyField(User, related_name = 'relationships')
      to_user = ForeignKeyField(User, related_name = 'related_to')
  
      class Meta:
          database = DATABASE
          indexes = ((('from_user', 'to_user'), True))
  </code></pre>
  
  <p>I haven't included the functions inside the class as I don't think it's needed. I don't want to clutter with code. Please tell me if you guys need it. Here's the error. (I found questions with similar errors but I still coulnd't figure out what's wrong in mine)</p>
  
  <pre><code>Traceback (most recent call last):
  File "app.py", line 175, in &lt;module&gt;
    models.initialize()
  File "/home/devang/Projects/Web-Apps/Flask/The Social Network/models.py", line 91, in initialize
    DATABASE.create_tables([User, Post, Relationship], safe=True)
  File "/usr/local/lib/python2.7/dist-packages/peewee.py", line 2602, in create_tables
    model.create_table(**options)
  File "/usr/local/lib/python2.7/dist-packages/peewee.py", line 5317, in create_table
    cls._schema.create_all(safe, **options)
  File "/usr/local/lib/python2.7/dist-packages/peewee.py", line 4593, in create_all
    self.create_indexes(safe=safe)
  File "/usr/local/lib/python2.7/dist-packages/peewee.py", line 4522, in create_indexes
    for query in self._create_indexes(safe=safe):
  File "/usr/local/lib/python2.7/dist-packages/peewee.py", line 4511, in _create_indexes
    for index in self.model._meta.fields_to_index()]
  File "/usr/local/lib/python2.7/dist-packages/peewee.py", line 4842, in fields_to_index
    fields.append(self.combined[part])
  KeyError: 'f'
  </code></pre>
  
  <p>Thank you!</p>