Generating Relationship model for following Users. 

$ rails generate model Relationship follower_id:integer followed_id:integer
Adding indices for the relationships table so that a user cannot follow another user more than once. Migrating the database.
Implementing the users has_many association
Tests and code for user/relationships belong_to association.
Adding the Relationship model validations.
 Adding the User model followed_users association.
The following? and follow! utility methods.
 Unfollowing a user by destroying a user relationship.
 Implementing user.followers using reverse relationships.
 Adding following/follower relationships to the sample data.
Adding following and followers actions to the Users controller.
 Testing the following/follower statistics on the Home page. Adding SCSS styling for the home page sidebar.
Adding routes for user relationships.
Partials for following and unfollowing users.
Adding the following and followers pages.
Tests for the Follow/Unfollow button.
Make the follow button working with Ajax.
Adding feed to the status model.
Returns micropost from the User.
The final implementation of from_users_followed_by.