title: Rails Many to Many with Extra Column
body: <p>So I have these tables:</p>
  
  <pre><code>create_table :users do |t|
    t.string :username
    t.string :email
    t.string :password_digest
  
    t.timestamps
  end
  
  create_table :rooms do |t|
    t.string :name
    t.string :password
    t.integer :size
    t.integer :current_size
  
    t.timestamps
  end
  
  create_table :rooms_users do |t|
    t.belongs_to :user, index: true
    t.belongs_to :room, index: true
  
    t.boolean :is_admin
  
    t.timestamps
  end
  </code></pre>
  
  <p>I made it so, when I call Room.find(1).users I get a list of all the users in the room. However, I also want to be able to call something like Room.find(1).admins and get a list of users that are admins (where is_admin in rooms_users is true). How would I do that? </p>
  
  <p>Thank you for your time!</p>