After a considerable amount of testing, I finally discovered the reason behind this error. The client connection explicitly set ANSI_WARNINGS and CONCAT_NULL_YIELDS_NULL OFF. XML data operations, such as @data.value('(/EVENT_INSTANCE/EventType)[1]', 'nvarchar(100)'), require both to be ON. I had attempted to override these within the trigger, but I may have placed them wrong. The final code below works, even with the explicit SET options in the connections from Great Plains:
CREATE TRIGGER [ddl_log]
ON ALL SERVER
FOR DDL_DATABASE_LEVEL_EVENTS, DDL_SERVER_LEVEL_EVENTS
AS
BEGIN
SET NOCOUNT ON;
SET ANSI_WARNINGS, CONCAT_NULL_YIELDS_NULL ON;
DECLARE @data XML
SET @data = EVENTDATA()
EXECUTE AS LOGIN='<dummy login>'
INSERT admin.dbo.ddl_audit (PostTime, DB_User, [Event], [TSQL], Host, DatabaseName)
VALUES (
GETDATE(),
CONVERT(NVARCHAR(100), ORIGINAL_LOGIN()),
@data.value('(/EVENT_INSTANCE/EventType)[1]', 'nvarchar(100)'),
@data.value('(/EVENT_INSTANCE/TSQLCommand)[1]', 'nvarchar(2000)'),
CONVERT(NVARCHAR(100), HOST_NAME()),
@data.value('(/EVENT_INSTANCE/DatabaseName)[1]','nvarchar(100)')
) ;
REVERT
END
As an alternative, I also could have simply inserted EVENTDATA() as an XML LOB into a table, rather than parsing it out into columns. Because I would not be manipulating the XML, the SET options do not matter. Then I would just build an XML index for querying performance, and construct a view to use for audit log reporting that parses the XML in the view definition, in the same manner as I am doing above in my INSERT statement.
Thanks to Max for pointing me in a different research direction, and @AaronBertrand on #sqlhelp who helped me with correct SET options within the body of the trigger.
Best Answer
You can extract much more data from the event instance in the Service Broker message to store in the table. Specifically, TargetLoginName should bring back the affected user for you, something like this should work:
More info here.