title: Entity Framework referential integrity not being enforced
body: <p>Using EF6, I have two tables in an SQL database and I've used database first to create the EF diagram from the database.</p>
  
  <p>My database is missing a foreign key constraint between the PK of one table and a foreign key in the other.</p>
  
  <p>Rather than add the foreign key constraint into the database I created it as an association in the EF model. </p>
  
  <p>The association looks good in the EF model, it has the correct principal and dependant.</p>
  
  <p>However if I delete a row from the principal table when dependants are present, referential integrity doesn't kick in and the principal row gets deleted.</p>
  
  <p>I know I can just add the relationship into the SQL database and update model from database. But I'd like to understand the scope of functionality of EF and whether it should be possible to add a relationship in the EF model but not in the SQL database and for it to still work?</p>
  
  <p>It seems to me that if the association (relationship) exists in EF but not in MSSQL, then the association is ignored for referential integrity when you delete a row via EF?</p>