Last week the inevitable happened. I created a page in C/Side with an ID that I had already been used by an extension.

Microsoft is aware of this issue but does not want to prevent it from happening.

The problem is that at first everything seems to work. Your new C/Side page will run just fine. I only noticed it after a restart of the Service Tier because this actually does a check but you have to dive into the Windows Event log to find it.

The Fix

Extension objects are stored in the NAV App Object Metadata table. You can write a SQL Trigger that checks if a record exists in that table with the same ID and Type. This should show a message like this.

The Trigger can look something like this:

USE [NAV] -- change DB Name here 
GO

IF EXISTS (SELECT * FROM sys.triggers WHERE object_id = OBJECT_ID(N'[dbo].[CheckExtensionObject]')) 
DROP TRIGGER [dbo].[CheckExtensionObject] 
GO 
CREATE TRIGGER [CheckExtensionObject] ON [dbo].[Object] 
AFTER INSERT
AS 
SET NOCOUNT ON 
 
DECLARE @ins_count int 
SELECT @ins_count = COUNT(*) FROM inserted 
 
IF (@ins_count <> 0) --BEGIN

IF ((select count(*) from [inserted] inner join [dbo].[NAV App Object Metadata] obj 
 ON obj.[Object Type] = inserted.[Type] AND obj.[Object ID] = inserted.[ID]) <> 0)
 RAISERROR('Object Already Exist as an Extension Object', 18, -1, '');
 
SET NOCOUNT OFF 
GO

With thanks to Jorg Stryk.