>> params['UserAttr']['3'] 
=> {"op"=>"+=", "type"=>"check", "value"=>"cd", "user_id"=>1, "attribute_id"=>"42"}
>> attribute = UserAttr.new(params['UserAttr']['3'])
ActiveRecord::AssociationTypeMismatch: Attribute expected, got Array

+--------------+-----------------------+------+-----+---------------------+----------------+
| Field        | Type                  | Null | Key | Default             | Extra          |
+--------------+-----------------------+------+-----+---------------------+----------------+
| id           | int(11)               | NO   | PRI | NULL                | auto_increment |
| user_id      | int(11)               | NO   | MUL | NULL                |                |
| attribute_id | int(11)               | NO   | MUL | NULL                |                |
| op           | varchar(2)            | NO   |     | NULL                |                |
| value        | varchar(253)          | NO   |     | NULL                |                |
| created_on   | timestamp             | YES  |     | 0000-00-00 00:00:00 |                |
| updated_on   | timestamp             | YES  |     | CURRENT_TIMESTAMP   |                |
| type         | enum('reply','check') | NO   |     | NULL                |                |
+--------------+-----------------------+------+-----+---------------------+----------------+