级联删除-映射到表的复杂类型

Question

Please consider the following relationship:

Car (entity) 1 ----------------------> * Wheels (Entity)

Wheel (entity) 1 --------->1 Nut (Complex type)

Wheel (entity) 1 --------->1 Rim (complex type)

Both Nut and Rim complex types are mapped to tables named Nuts and Rims. I am using Wheel ID as Nuts and Rims primary key.

Now, when attempting to delete Car using code, I get the following exception:

System.InvalidOperationException: 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.
at System.Data.Entity.Core.Objects.ObjectContext.PrepareToSaveChanges(SaveOptions options)
at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesInternal(SaveOptions options, Boolean  executeInExistingTransaction)
at System.Data.Entity.Core.Objects.ObjectContext.SaveChanges(SaveOptions options)
at System.Data.Entity.Internal.InternalContext.SaveChanges()
at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
at System.Data.Entity.DbContext.SaveChanges()

When attempting to do this in MS- SSMS, I get this error: The DELETE statement conflicted with the REFERENCE constraint "FK_dbo.Nuts_dbo.Wheel_Id". The conflict occurred in database "DatabaseName", table "dbo.Nuts", column 'Id'.

Given, that complex types are required parameters for an entity and have a one-to-one relationship, why wouldn't cascade delete be ON by default in this scenario? Second, how should go about deleting CAR and its related many Wheels along with all associated Nuts and Rims. Lastly, in my case, a car has thousands of wheels. Is it a good idea to this in code or to use stored procedures?

Thanks.

Answer 1

As Ben Robinson mentions in his comment, the purpose of classes attributed with [ComplexType] is to have their properties mapped to columns within the table of the containing type. There should be no Nut or Rim tables. If this isn't the desired behaviour then they shouldn't be complex types.

Let's assume they shouldn't be complex types and work out why they are not cascade deleting. Concentrating on Nut, and assuming you are not using fluent configuration, I suspect you would need to have a navigation property to Wheel on the Nut, as well as the WheelId. The WheelId would be marked with [Key] and [ForeignKey(Wheel)], I think. The main point is the navigation property.

With fluent configuration you would have the navigation property to Wheel and then, in the configuration for Wheel, you would have:

HasRequired(wheel => wheel.Nut)
  .WithRequiredDependent(nut => nut.Wheel);

Another point to note is that the cascade delete, if it isn't generated to your taste, can be modified inside a migration in the foreign key creation via a method argument.

Finally, to answer your question about batch delete: Cascade delete will be done in the database if you delete the Car and it cascade deletes the Wheel, and that should be fast. If you want to perform deletes of many wheels for a car separately then have a look at Entity Framework Extensions: http://efe.codeplex.com/