gistfile1.rb

ActiveRecord::Schema.define(:version => 20120620132905) do
  create_table "tasks", :force => true do |t|
    t.string  "name"
    t.integer "sender_id"
    t.integer "receiver_id"
  end

  create_table "users", :force => true do |t|
    t.string "name"
  end
end

class Task < ActiveRecord::Base
  attr_accessible :name, :receiver, :sender

  belongs_to :sender, :class_name => 'User'
  belongs_to :receiver, :class_name => 'User'
end

class User < ActiveRecord::Base
  attr_accessible :name

  has_many :sent_tasks, :class_name => 'Task',
    :foreign_key => 'sender_id', :inverse_of => :sender
  has_many :received_tasks, :class_name => 'Task',
    :foreign_key => 'receiver_id', :inverse_of => :receiver
end

1.9.3p194 > User.create! :name => 'First'
 => #<User id: 1, name: "First">

1.9.3p194 > User.create! :name => 'Second'
 => #<User id: 2, name: "Second">

1.9.3p194 > Task.create! :name => 'Task 1', :sender => User.first, :receiver => User.last
 => #<Task id: 1, name: "Task 1", sender_id: 1, receiver_id: 2>

1.9.3p194 > User.first.sent_tasks
 => [#<Task id: 1, name: "Task 1", sender_id: 1, receiver_id: 2>]

1.9.3p194 > User.first.received_tasks
 => [] 

1.9.3p194 > User.last.sent_tasks
 => [] 

1.9.3p194 > User.last.received_tasks
 => [#<Task id: 1, name: "Task 1", sender_id: 1, receiver_id: 2>]