每个类型的表继承插入问题

Question

I followed this article on making a table-per-type inheritance model for my entities, but I ran into some issues. Below I'm posting steps to reproduce the problem I'm having in a minimal environment to rule out other factors.

First, I created a new MS SQL Server 2008 R2 database with the following two tables:

Users

• Id : bigint (PK and set it as the identity column)
• Name : nvarchar(25) NOT NULL (whatever, some random property

Customers

• Id : bigint (PK, identity column, and FK on Users.Id)
• Title : nvarchar(25) NOT NULL (also whatever, some random property)

Next, I generated the .edmx entity model from the database, and followed the link at the top verbatim. That is to say, I deleted the association between User and Customer, set User as the base class of Customer, deleted the Id property from the Customer entity, and made sure that the Customer.Id column was mapped to the inherited User.Id property. I then ran the following small program:

using (var db = new EF_Test.testEntities())
{
    var cust = db.Users.CreateObject<Customer>();
    db.Users.AddObject(cust);
    db.SaveChanges();
}

I get the following error when I make that last call:

"A value shared across entities or associations is generated in more than one location. Check that mapping does not split an EntityKey to multiple store-generated columns."

With the following inner exception:

"An item with the same key has already been added."

Any ideas on what I could be missing?

Answer 1

A quick google on the error message turned up the following solution, maybe it helps you:

http://social.msdn.microsoft.com/Forums/en/adodotnetentityframework/thread/4bfee3fd-4124-4c1d-811d-1a5419f495d4

I think that I figured it out. The table for the Party sub type had its key column set to autogenerate a key value and since it's derived, the EF wanted to set that value explicitly.

So have you tried removing the "identity" setting from the customer table? So it doesn't autogenerate the primary key?

Hope this helps.

Answer 2

I finally found the source of my troubles. For those still interested, in the Customers table, the Id column should not have been set to the identity column of the table (PK and the FK dependency are fine though).

Answer 3

Why you don't want to make a foreign key (UserId) as a separate column? Maybe it can help you. Also try to use model first approach and generate db after model creation as it is described in the following article .