I am using ES 2007.1.1210, with SQL Server provider (connecting to SQLExpress 2005 for dev/testing) and VS 2005/VB.NET

I have added timestamp fields to the tables and regenerated the classes in order to have concurrency exceptions thrown when editing collisions occur.

I use a vb.net unit test based on the ES unit test to check that concurrent editing raises an exception (see below). However, although the record doesn't get overwritten the exception is not raised.

Is something required to switch on concurrency exceptions?

This is the table definition: 

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
IF NOT EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[clients]') AND type in (N'U'))
BEGIN
CREATE TABLE [clients](
	[id] [int] IDENTITY(1,1) NOT NULL,
	[student_id] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[first_name] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[last_name] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL,
	[phone] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[mobile] [varchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[timestamp] [timestamp] NOT NULL,
	
	[created] [datetime] NOT NULL,
	[modified_by] [int] NOT NULL,
 CONSTRAINT [PK_clients] PRIMARY KEY CLUSTERED 
(
	[id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, 

IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON)
)
END
GO

Here is the unit test code I am using (based directly on the ES test):

        Dim test_id As Integer

        Try
            Dim c As New BusinessObjects.Clients
            c.AddNew()
            c.FirstName = String.Format("FIRSTNAME {0}", 1)
            c.LastName = String.Format("LASTNAME {0}", 1)
            c.StudentId = String.Format("11")
            c.ModifiedBy = Me._support.StaffUser.Id
            c.Save()

            test_id = c.Id

            c = New BusinessObjects.Clients
            c.LoadByPrimaryKey(test_id)
            c.FirstName = "MODIFIED BY 1"

            Dim c2 As New BusinessObjects.Clients
            c2.LoadByPrimaryKey(test_id)
            c2.FirstName = "MODIFIED BY 2"

            c.Save() ' written to db
            c2.Save() ' not written to db, but no exception!

            Assert.Fail("Concurrency exception not thrown")

        Catch cex As EntitySpaces.Interfaces.esConcurrencyException
            Assert.AreEqual("Error", cex.Message.ToString.Substring(0, 5))
        Catch ex As Exception
            Assert.Fail(ex.ToString)
        Finally
            Dim c As New BusinessObjects.Clients
            c.LoadByPrimaryKey(test_id)
            c.MarkAsDeleted()
            c.Save()
        End Try

Your code looks fine, here is our unit test that is passing just fine:

try
{
	// Setup
	ComputedTest entity = new ComputedTest();
	entity.AddNew();
	entity.Save();
	testId = entity.Id.Value;

	// Test
	entity = new ComputedTest();
	entity.LoadByPrimaryKey(testId);
	entity.str.SomeDate = "2007-01-01";

	ComputedTest entity2 = new ComputedTest();
	entity2.LoadByPrimaryKey(testId);
	entity2.str.SomeDate = "1999-12-31";

	entity.Save();
	entity2.Save();
	Assert.Fail("Concurrency Exception not thrown.");
}
catch (EntitySpaces.Interfaces.esConcurrencyException cex)
{
	Assert.AreEqual("Error", cex.Message.ToString().Substring(0, 5));
}
catch (Exception ex)
{
	Assert.Fail(ex.ToString());
}
finally
{
	// Cleanup
	ComputedTest entity = new ComputedTest();
	entity.LoadByPrimaryKey(testId);
	entity.MarkAsDeleted();
	entity.Save();
}
break;

I wonder if naming your column "timestamp" could be causing an issue? not likely but that caught my eye. Are you using stored procedures? If so you would need to regenerate those also.

That test can fail in one of two ways. If no exception at all is thrown in the "try" block, the test will fail with the specific message in NUnit, "Concurrency Exception not thrown." If any exception other than a concurrency exception is thrown in the "try" block, then the second "catch" block will pass on the exception to NUnit.

Your CREATE TABLE has a datetime field [created] that is defined NOT NULL, but has no default specified. Based on that, the very first c.Save() should throw a "column does not allow nulls. INSERT fails." exception. Nothing should be saving to the database.

I accidently failed to post part of the table definition which sets a default getdate() value for the created field. Please be assured that the record is being saved.

The test is failing with the 'concurrency exception not thrown' - no exception is being thrown.
 

Do you have the following attribute set in your config file?

databaseVersion="2005"

If using stored procedures, did you regen with "SQL Server 2005" checked in the SQL Server SP template?

Yes, databaseVersion="2005" in config. The s/w is not using stored procedures.

The timestamp change is being recognised at some level, as the second save (c2.save) does not update the record. However, even though this save fails, no exception is raised.

I have tried tracing into the save, but quickly got lost in a maze of getmeta.. things and couldn't see anywhere where the save was failing. 

It appears that an UPDATE trigger containing an INSERT breaks the concurrency exceptions. I hope there is a work-around as otherwise I have to trade collision detection for audit trails!

Here's the test trigger I used, with a dummy table to ensure that it wasn't related to the specific audit tables:

CREATE TABLE [dbo].[ttable](
	[col1] [varchar](50) NOT NULL
) ON [PRIMARY]

GO

CREATE TRIGGER tu_clients ON [dbo].[clients] FOR UPDATE 
NOT FOR REPLICATION
AS
BEGIN

INSERT INTO ttable (col1) values('hello world');

END
GO

With this trigger no exception is raised.

Without the trigger the collision exception is raised.

With the trigger without an INSERT statement the collision exception is raised.

Am I missing something blindingly obvious here?
 

Wow, good job tracking this down. I know why you're not getting the exception. The reason why is that ADO.NET throws the exception if you try to do an update or a delete and the rows effected equals zero. This indicates to ADO.NET that the update/delete didn't occur which could only indicate a concurrency exception. However, because you are doing an INSERT in the trigger the rows effected are 1, so no exception is thrown (even though the ES code correctly refused to update). I wonder if you can just do a SET NOCOUNT in the trigger to avoid this?

Thanks Mike, SET NOCOUNT solved it.

For future reference for anyone else using an UPDATE or DELETE trigger for audit trails, this toy trigger now passes the test, inserting a single record to ttable, and raising the exception on the second save:

ALTER TRIGGER [dbo].[tu_clients] ON [dbo].[clients] FOR UPDATE 
NOT FOR REPLICATION
AS
BEGIN
set nocount on;

INSERT INTO ttable (col1) values('hello world');

set nocount off;

END