Here are some notes on how to create a has_many relationship and the corresponding APIs for each entity.

> rails new hasMany
> rails g scaffold User name:string
> rails g scaffold Micropost content:string user_id:integer

user.rb

class User < ActiveRecord::Base
   has_many :microposts, dependent: :destroy
   end

micropost.rb

class Micropost < ActiveRecord::Base
  belongs_to :user
end

Sample calls

> micropost.user
> user.microposts
> user.microposts.create(arg)
> user.microposts.build
> @micropost = user.microposts.build(content: “Lorem ipsum”)

Links that help
http://ruby.railstutorial.org/book/ruby-on-rails-tutorial#sec-demo_user_has_many_microposts