EF Many to Many cascading delete - entity-framework

Question

I have an issue.
I have some classes that look like this:
public class Question
{
public int Id { get; set; }
[Required] [MaxLength(255)] public string Text { get; set; }
public int CriteriaId { get; set; }
public int QuestionGroupId { get; set; }
public QuestionGroup QuestionGroup { get; set; }
public virtual IList<Answer> Answers { get; set; }
public virtual Criteria Criteria { get; set; }
}
public class Answer
{
public int Id { get; set; }
[Required] [MaxLength(255)] public string Text { get; set; }
public int QuestionId { get; set; }
public Question Question { get; set; }
public virtual IList<State> States { get; set; }
}
public class Criteria
{
public int Id { get; set; }
[Required] [MaxLength(100)] public string Name { get; set; }
public virtual IList<State> States { get; set; }
public IList<Question> Questions { get; set; }
}
public class State
{
public int Id { get; set; }
public int CriteriaId { get; set; }
[Required] [MaxLength(100)] public string Name { get; set; }
public int Score { get; set; }
public virtual IList<Filter> Filters { get; set; }
public Criteria Criteria { get; set; }
}
They have a many to many relationship, so I created this mapping:
modelBuilder.Entity<Answer>()
.HasMany(m => m.States)
.WithMany()
.Map(m => {
m.MapLeftKey("AnswerId");
m.MapRightKey("StateId");
m.ToTable("AnswerStates");
});
When I tried to update my database I get an error about foreign keys.
So I added this line (as a temporary fix):
modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();
But I need the cascading delete.
I can't seem to figure out why it won't let me have it.
The error I get when trying to include cascading deletes is:
Introducing FOREIGN KEY constraint 'FK_dbo.AnswerStates_dbo.States_StateId' on table 'AnswerStates' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
I hope I have provided enough information. Does anyone know what I can do to allow the cascading delete (I need to be able to delete a State or an Answer and it to remove the record from AnswerStates

Answer 1

This is pretty much the same as another question (Deleting only one entry from Many-to-Many relationship) I was answering today. Just your case is a bit more complicated.
The multiple cascade path in your case is from Criteria to AnswerStates. When deleting a Criteria record, the AnswerStates records can be deleted either by Criteria->States->AnswerStates or Criteria->Questions->Answers->AnswerStates relationships.
The solution is always one and the same - turn one of the relationships cascade delete off and handle deletion either manually or via trigger.
In this particular case, my suggestion is to turn Criteria->States cascade delete off:
modelBuilder.Entity<Criteria>()
.HasMany(m => m.States)
.WithRequired(d => d.Criteria)
.HasForeignKey(d => d.CriteriaId)
.WillCascadeOnDelete(false);
and use something like this before deleting a Criteria:
db.States.RemoveRange(db.States.Where(s => s.CriteriaId == criteriaId_to_be_removed));