DELETE statement conflicted in Database First - sql

Question

Let's say I have a database with table A and table B. B has a foreign key to table A, which does not allow nulls. When I try to delete and entity of A I want all references in table B to be removed as well. I try to do this with the following code:
using (var ctx = new MyDatabaseContext(ConnectionString))
{
var a= new A() { IdA= idA};
ctx.A.Attach(a);
ctx.A.Remove(a);
ctx.SaveChanges();
}
This results in the following error message:
Additional information: The DELETE statement conflicted with the REFERENCE constraint "FK_B_A". The conflict occurred in database "MyDatabase", table "dbo.B", column 'IdA'.
The statement has been terminated.
I have tried a lot, from using Triggers in the database to defining the ON DELETE CASCADE, but Entity Framework does fail. What am I doing wrong?
Trigger:
ALTER TRIGGER [dbo].[trg_DelA]
ON [dbo].[A]
FOR DELETE AS
BEGIN
DELETE FROM B WHERE B.IdA = IdA;
END
BTW: This is just an example. The actual database is larger and also contains intermediate tables for many to many relationships.
BR
Thomas

Answer 1

AFTER (or FOR - they are synonyms) trigger are fired after triggering SQL statement. In your case this is too late, since deleting statement can't be completed due to foreign keys.
If you want to use trigger to handle cascade deletion - you have to use instead of trigger, and in this trigger first delete records from B table and then from A table.
So this could look like:
CREATE TRIGGER [dbo].[trg_DelA]
ON [dbo].[A]
INSTEAD OF DELETE AS
BEGIN
DELETE FROM B WHERE B.IdA in (select IdA from deleted)
DELETE FROM A WHERE IdA in (select IdA from deleted)
END
See MSDN for reference.

Answer 2

Cascade your deletes.
Take a look at this: Entity framework code first delete with cascade
And this: https://msdn.microsoft.com/en-us/library/hh295843(v=vs.103).aspx