Department hasMany Employees

Below is my employee migration class

class CreateEmployees < ActiveRecord::Migration
  def self.up
    create_table :employees do |t|
      t.references :department
      t.string :first_name
      t.string :last_name
      t.string :mobile_number
      t.string :email
      t.text :description

      t.timestamps
    end
  end

  def self.down
    drop_table :employees
  end
end

notice the "t.references :department" which is actually a reference to department model