DataMapper | Unknown column 'User' in 'field list'

[eluser]thomasjonas[/eluser]
Hello there,

I'm new to Datamapper and I'm straight diving into the advanced relations. Unfortunately it's not working out so great for me... Somehow I keep getting this error:

Code:

Unknown column 'User' in 'field list'

INSERT INTO `posts` (`title`, `creator`, `editor`) VALUES ('testing', User, User)

Filename: ........................../libraries/Datamapper.php

Line Number: 1724

I'm using CI 2.1.0

This is how my User model looks like:

Code:

class User extends DataMapper {
    var $has_many = array(
        'created_post' => array(
            'class' => 'post',
            'other_field' => 'creator'
        ),
        'edited_post' => array(
            'class' => 'post',
            'other_field' => 'editor'
        )
    );

var $validation = array(
        'username' => array(
            'label' => 'Username',
            'rules' => array('required', 'trim', 'unique', 'alpha_dash', 'min_length' => 3, 'max_length' => 20),
        ),
        'password' => array(
            'label' => 'Password',
            'rules' => array('required', 'min_length' => 6, 'encrypt'),
        ),
        'email' => array(
            'label' => 'Email Address',
            'rules' => array('required', 'trim', 'valid_email')
        )
    );
}

Post model

Code:

class Post extends DataMapper {
    var $has_one = array(
        'creator' => array(
            'class' => 'user',
            'other_field' => 'created_post'
        ),
        'editor' => array(
            'class' => 'user',
            'other_field' => 'edited_post'
        )
    );

var $validation = array(
     'title' => array(
         'label' => 'Title',
         'rules' => array('required')
     )
);
}

Controller

Code:

$u = new User(1);

  $p = new Post();
  $p->title = "testing";
  $p->save_creator($u);
  $p->save();

In my database there already is a user with id=1

Database:
users:
-id
-username
-password
-email

posts:
-id
-title
-creator
-editor

posts_users
-id
-creator_id
-created_post_id
-editor_id
-edited_post_id

Hopefully it's a really stupid mistake that can be fixed easily...
Thanks in advance!