title: How to add a particular migration with multiple entries in rails
body: <p>I want to create a new field in my rails database which has multiple fields associated with it and can take multiple sets of entries. For example in Linkedin,</p>
  
  <p>a user adds a job with information like title, description and duration and can create multiple jobs associated to his profile.</p>
  
  <p>How do I build a similar system in rails, is it possible using only migrations or do I have to create a new model for it and associate it with a particular user.</p>
  
  <p>Which will be the correct way to go through this issue?</p>