title: MagicalRecord: one to many relationship
body: <p>I m not quite sure if it is the right approach</p>
  
  <p>I want to have a one to many relationship between entity A and B, so A could refer to multiple records of B, but B only to one record of A</p>
  
  <p>my question is how to do this with MagicalRecords... i m familiar with the basic fetching and creating of single entities</p>
  
  <p>but have no clue how to fetch, creat, update entities with realtionships</p>