Is there an activerecord relationship to solve this problem? - ruby-on-rails

Question

I can't seem to wrap my head around this. I have three tables:
mysql> desc users;
+----------------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| username | varchar(255) | YES | | NULL | |
+----------------------+--------------+------+-----+---------+----------------+
mysql> desc mentions;
+------------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| message_id | int(11) | YES | | NULL | |
| mentionable_type | varchar(255) | YES | | NULL | |
| mentionable_id | int(11) | YES | | NULL | |
+------------------+--------------+------+-----+---------+----------------+
mysql> desc messages;
+------------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+----------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| body | text | YES | | NULL | |
| user_id | int(11) | YES | | NULL | |
+------------+----------+------+-----+---------+----------------+
And the following relationships:
class User < ActiveRecord::Base
has_many :messages
end
class Message < ActiveRecord::Base
belongs_to :user
has_many :mentions
end
class Mention < ActiveRecord::Base
belongs_to :mentionable, :polymorphic => true
belongs_to :message
end
I'm not sure if I'm using it correctly, but I used the polymorphic relationship in Mention because mentionable_type could be 'User' or 'Group'. I've left the Group stuff out of this post as it's not related to this question.
When a user creates a Message, their user_id is stored in the messages table. I can easily return a list of a user's "authored" messages with:
current_user.messages
Similar to a tweet, the message's body may, or may not, contain mentions of n users or groups. When the message "I'm having lunch with #userA, #userB, and #groupX." is created, the body would be parsed and those three "mentions" would be created as well.
I can easily return all of a user's "mentions" with:
current_user.mentions
If I want to see the message of a mention, I can do:
mention = current_user.mentions.first
mention.message
What I can't seeem to figure out is a clean way to combine the two and get a list of messages that a user created AND were mentioned in. Any ideas?

Answer 1

I your User model, this line should be present for polymorphic relationships.
class User
has_many :messages
has_many :mentions, :as => :mentionable
end
And try this:
user_id = 10
#messages = Message.find(:all, :joins => [:mentions],
:conditions => ['messages.user_id = ?', user_id])