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<Card>()
    .HasRequired(c => c.Stage)
    .WithMany()
    .WillCascadeOnDelete(false);

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

Answer 2

Just for documentation purpose, to someone that comes on the future, this thing can be solved as simple as this, and with this method, you could do a method that disabled one time, and you could access your method normally

Add this method to the context database class:

protected override void OnModelCreating(DbModelBuilder modelBuilder) {
    modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
}

Answer 3

I had this issue also, I solved it instantly with this answer from a similar thread

In my case, I didn't want to delete the dependent record on key deletion. If this is the case in your situation just simply change the Boolean value in the migration to false:

AddForeignKey("dbo.Stories", "StatusId", "dbo.Status", "StatusID", cascadeDelete: false);

Chances are, if you are creating relationships which throw this compiler error but DO want to maintain cascade delete; you have an issue with your relationships.

Answer 4

You can set cascadeDelete to false or true (in your migration Up() method). Depends upon your requirement.

AddForeignKey("dbo.Stories", "StatusId", "dbo.Status", "StatusID", cascadeDelete: false);

Answer 5

The existing answers are great I just wanted to add that I ran into this error because of a different reason. I wanted to create an Initial EF migration on an existing DB but I didn't use the -IgnoreChanges flag and applied the Update-Database command on an empty Database (also on the existing fails).

Instead I had to run this command when the current db structure is the current one:

Add-Migration Initial -IgnoreChanges

There is likely a real problem in the db structure but save the world one step at a time...

Answer 6

This sounds weird and I don't know why, but in my case that was happening because my ConnectionString was using "." in "data source" attribute. Once I changed it to "localhost" it workded like a charm. No other change was needed.