Constrain the number of child entities in Entity Framework

Question

Bottom Line Up Front

Is there a succinct way that I can constrain the number of child entities that can belong to a parent in Entity Framework. I am using 4.3.1 at th

Answer 1

There is no built-in way so you will have to code such validation yourselves. Some quick ideas:

• You can for example use custom collection for the navigation property which will fire exception when you try to add additional search exceeding the threshold. It is simple but it demands you to have all searches loaded, it will have concurrency problems and moreover it can fire during loading search list and searches from database.
• You can handle it in overriden SaveChanges. You will at least have to check how many searches are already related to search list but you will still have concurrency problem (what if other request tries to add search to the same list but only one place is remaining - both can succeed the check and insert related search)
• You can handle it in database trigger - again it will have concurrency problems

Avoiding concurrency problems completely requires hand written queries with locking hints to ensure that only one request can check number of searches per search list and insert a new search in atomic transaction.