title: Correct way to maintain a One to many relation with fixed count of children rows?
body: <p>I am modeling a common one to many relation between an Authors table and a Books table.</p>
  
  <p>By convention, an Author can have 30 books assigned as a maximum. So, when an author gets its max number of books and another one want to be assigned to the same author, I must delelete oldest one and add new one.</p>
  
  <p>I could do the obvious operation of delete de oldest book and add the new one to keep the 30 books limit but I wonder if it is a more direct way to do this or if this is common practice in this situation.</p>