Entity Framework on delete cascade

问题:

I have problem with deleting related rows in Entity Framework 4.1. I have tables with relations

Book 1<--->* BookFormats

I have set the on delete cascade:

ALTER TABLE [dbo].[BookFormats]  WITH CHECK ADD  CONSTRAINT [FK_BookFormats_Book] 
FOREIGN KEY([BookID]) REFERENCES [dbo].[Book] ([BookID]) on delete cascade

The EDMX property

Then, I want to remove the all BokFormats items related to my Book object:

 var originalBook = m.db.Book.First(x => x.BookID == bookId);
 originalBook.BookFormats.Clear();
 m.db.SaveChanges();

But, I get the error:

The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted.

I ran out of ideas on how to delete these objects. Any ideas?

回答1:

Cascade deletions concept is as follows:

When you delete Book from the DB all related BookFormats will be deleted for you by SQL Server (please note that it doesn't matter how deletion of Book will be initiated via EF or raw SQL). Thus it has nothing to do with your task: "I want to delete all BookFormats related to my Book". To accomplish it you need something like this:

foreach(var m in m.db.BookFormats.Where(f=>f.BookID == bookID))
{
    m.db.BookFormats.Remove(m);
}
m.db.SaveChanges();

回答2:

You can use RemoveRange :

m.db.BookFormats.RemoveRange(originalBook.BookFormats);
m.db.SaveChanges();

But this is for EF 6.0

回答3:

You are not deleting the BookFormats from the database, but you are removing the relationship, thus orpahning your BookFormats and setting the BookID column to NULL. The delete cascade you have put on the database says When I delete theBook, then delete all of theBookFormatsthat have aBookIDequal to mine. You are not deleting the book you are deleting the formats from the Book.

Instead of originalBook.BookFormats.Clear() you should have something like this...

List<int> idsToDelete = new List<int>();

foreach (BookFormat bf in originalBook.BookFormats)
{
    idsToDelete.Add(bf.ID);
}

foreach (int id in idsToDelete)
{
    BookFormat format = m.db.BookFormat.FirstOrDefault(x => x.ID == id);
    if (format != null)
    {
         m.db.DeleteBookFormat(format);
    }
}

m.db.SaveChanges();

It should be something along those lines. I don't have it right in front of me to remember how EF constructs the delete method in the EDMX.

回答4:

I've tested it in EF 6.1.3 and this should work fine:

 var originalBook = m.db.Book.First(x => x.BookID == bookId);
 originalBook.BookFormats.Clear();
 db.Books.Remove(originalBook);
 m.db.SaveChanges();

回答5:

I use EF6 and this works.

        var itemBinding = db.ItemBinding.Where(x => x.BindingToId == id) ;
        foreach (var ib in itemBinding)
        {
            db.Item.Remove(ib.Item);
            db.ItemBinding.Remove(ib);
        }
        db.SaveChanges();