title: Specifying a foreign key in JPA
body: <p>I currently have a table which looks like this:</p>
  
  <p>Users</p>
  
  <p>username
  address
  dob
  ...</p>
  
  <p>And</p>
  
  <p>Roles
  username
  role</p>
  
  <p>I want to make a foreign key constraint between Role.username and User.username. How should I go about doing this with ann</p>