使用Entity Framework 4.1，如何达到低于要求的水平？

Question

Consider I have 2 entities - a) Publisher b) Book Publisher has navigation property called as PublishedBooks which is collection of Books. Assume that Publisher1 has published 2 books ie Book1 & Book2 What I would like to do is, for a Publisher1, delete published book Book1 and add a new published book (ie Book3), in the database.

Context.SaveChanges() throwing below 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.

Note : Delete cascade rule is present in database as well as in the context class. BTW, I am using C# & Sql Server 2005.

Answer 1

Sounds like you are doing something like this:

Foo foo = entity.RelatedFoos.Where(f=>f.id=xyz);
entity.RelatedFoos.Remove(foo); //this is the problematic line
context.SaveChanges();

That is; you are removing an entity from a set of related items - not from the main collection on the context itself. As noted in the error, removing the above way only removes the relation . Not the object foo . This is probably what you meant, if you mean to delete the foo :

Foo foo = entity.RelatedFoos.Where(f=>f.id=xyz);
context.Foos.Remove(foo);
context.SaveChanges();

Answer 2

You need to explicitly delete the child object before the save, eg

Context.DeleteObject(Book1);
Context.SaveChanges();