Question

I am teaching myself the framework and have been messing with Active Record. I’m stuck with a problem that is easy to solve with raw SQL, and I’m wondering the best way to port it to Active Record …

I have the following database schema …

CREATE TABLE chats (
  id int(11) DEFAULT NULL,
  user_id int(11) DEFAULT NULL,
  more longtext
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

CREATE TABLE statuses (
  chat_id int(11) DEFAULT NULL,
  user_id int(11) DEFAULT NULL,
  is_read tinyint(1) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

CREATE TABLE users (
  id int(11) DEFAULT NULL,
  name varchar(255) DEFAULT NULL,
  mail varchar(255) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

And I want to do the following in Active Record where the 1 in the join is the current user ID …

SELECT 
c.*, s.is_read
FROM chats c
LEFT JOIN statuses s ON c.id = s.chat_id AND 1 = s.user_id

How do I set up this relationship so that I can have a simple ‘is read’ variable in my chat object? I know I can do this by performing various logic on the chat and status models I have but that seems far messier?

Answer 1

class Chat
  belongs_to :user
  has_one :status, :through => :user 
  scope :readed, joins(:status).where(:status => {:is_read => true})
  scope :unreaded, joins(:status).where(:status => {:is_read => false})

  delegate :is_read, :to => :status
end

class Status
  belongs_to :user
  belongs_to :chat
end

class User
  has_many :chats
  has_many :statuses
end

@current_user.chats.readed #=> select all user chats where chat status is_read = true
@current_user.chats.unreaded
@current_user.chats.first.is_read