EF上的InvalidOperationException

Question

I'm using WPF MVVM Pettern and I Have a simple table on SQL Server 2012 which its ID (key) column is computed in an StoredProcedure, called PersonInsert : (This is simplified, but what is computed is more complex than this, anyway it's an int at last)

USE [Guard]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE PROCEDURE [dbo].[PersonInsert]
@FName NVARCHAR(50) ,
@LName NVARCHAR(50) ,
@ID INT = NULL OUTPUT
AS
BEGIN
    BEGIN TRY
        SELECT  @ID = ISNULL(MAX(ID), 0) + 1
        FROM    dbo.Person


        INSERT  INTO [dbo].[Person]
                ( [ID] ,
                  [FName] ,
                  [LName] 
                )
        VALUES  ( @ID ,
                  @FName ,
                  @LName 
                )
    END TRY
    BEGIN CATCH
        DECLARE @ErrMsg NVARCHAR(MAX) ,
            @ErrSvr INT ,
            @ErrStt INT

        SELECT  @ErrMsg = ERROR_MESSAGE() + '|' + ERROR_PROCEDURE() + '|'
                + CAST(ERROR_LINE() AS NVARCHAR(5)) ,
                @ErrSvr = ERROR_SEVERITY() ,
                @ErrStt = ERROR_STATE()

        RAISERROR (@ErrMsg, @ErrSvr, @ErrStt)
    END CATCH
END
GO

In the .net side, I use EF 6.1 Code-First to handle data and mapped to SPs so I have OnModelCreating like this:

modelBuilder.Entity(Of Person)().MapToStoredProcedures(
                    Sub(x)
                          x.Insert(Function(e) e.HasName("[dbo].[PersonInsert]"))
                          x.Update(Function(e) e.HasName("[dbo].[PersonUpdate]"))
                          x.Delete(Function(e) e.HasName("[dbo].[PersonDelete]"))
                    End Sub)

And My Model is:

<Table("Person")> _
Partial Public Class Person

    <DatabaseGenerated(DatabaseGeneratedOption.None), Key> _
    Public Property ID As Integer

    Public Property FName As String
    Public Property LName as String
End Class

Now the strange thing is, when I try to Insert Data (Adding New Person) at first time, the db.SaveChanged() works great, but for second time it throws InvalidOperation exception with a message:

The changes to the database were committed successfully , but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: Saving or accepting changes failed because more than one entity of type 'Shoniz.Guard.WPFGuardApplication.Person' have the same primary key value. Ensure that explicitly set primary key values are unique. Ensure that database-generated primary keys are configured correctly in the database and in the Entity Framework model. Use the Entity Designer for Database First/Model First configuration. Use the 'HasDatabaseGeneratedOption" fluent API or ' DatabaseGeneratedAttribute ' for Code First configuration.

He is right! the data is comitted successfully! and I'm right too, because my ID (key) column is computed right and it's completely unique. Either I have used the DatabaseGeneratedAttribute with none value on ID, but the result is the same :(

Even when I re-query the db to check about duplicate keys, I find NOTHING!

1. Why this exception is thrown?
2. How can I prevent that?
3. Is there anyway to Ignore the changes after db.SaveChanges() ?

Answer 1

First of all change DatabaseGeneratedOption.None to DatabaseGeneratedOption.Indetity and finally change stored procedure to this:

BEGIN TRY
        SELECT  @ID = ISNULL(MAX(ID), 0) + 1
        FROM    dbo.Person


        INSERT  INTO [dbo].[Person]
                ( [ID] ,
                  [FName] ,
                  [LName] 
                )
        VALUES  ( @ID ,
                  @FName ,
                  @LName 
                )
        --You have to tell EF this is returned Id of inserted person
        SELECT @ID as ID
    END TRY