Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths - why?

Question

I\'ve been wrestling with this for a while and can\'t quite figure out what\'s happening. I have a Card entity which contains Sides (usually 2) - and both Cards and Sides h

Answer 1

Because Stage is required, all one-to-many relationships where Stage is involved will have cascading delete enabled by default. It means, if you delete a Stage entity

• the delete will cascade directly to Side
• the delete will cascade directly to Card and because Card and Side have a required one-to-many relationship with cascading delete enabled by default again it will then cascade from Card to Side

So, you have two cascading delete paths from Stage to Side - which causes the exception.

You must either make the Stage optional in at least one of the entities (i.e. remove the [Required] attribute from the Stage properties) or disable cascading delete with Fluent API (not possible with data annotations):

modelBuilder.Entity()
    .HasRequired(c => c.Stage)
    .WithMany()
    .WillCascadeOnDelete(false);

modelBuilder.Entity()
    .HasRequired(s => s.Stage)
    .WithMany()
    .WillCascadeOnDelete(false);