Using the EventData() Function with DDL triggers in SQL Server 2005

Solution

In SQL Server 2005, you can get data regarding the event that initiated the DDL trigger by accessing the EventData()function. This function returns information about server or database events and is stored in a variable that uses the XML data type. What we need to do is capture the data returned by the EventData() function and store it in a database table for reporting purposes.

You can store that data directly in an XML column or process it first before storing it as ordinary columns in a table. But since the returned type is XML, we need to apply a bit of XQuery against the data generated by the function. To identify the elements in the XML data returned, use Index or Search to locate the topic for the event in SQL Server Books Online. For this particular tip, we will use table-related events. TheDDL_TABLE_EVENTS type describes what data can be captured for a CREATE, ALTER or DROP TABLE event.

Let's use the Northwind database for this example. We will create a table that will store the data returned by the EventData() function. We will only choose a few items from the schema generated by the ALTER_TABLE event; namely, the TSQLCommand, PostTime, LoginName, and EventType which is included in every event.

Create the event log table

USE Northwind   GO  CREATE TABLE EvtLog  (      PostTime DATETIME,      LoginName NVARCHAR(100),      EventType NVARCHAR(100),      TSQLCommand NVARCHAR(2000)    )  GO

Create the DDL trigger

CREATE TRIGGER trPreventTblChange   ON DATABASE    FOR ALTER_TABLE  AS   DECLARE @Data XML  SET @Data = EventData()  INSERT EvtLog (PostTime, LoginName, EventType, TSQLCommand)   VALUES       (GETDATE(),       CONVERT(NVARCHAR(100), CURRENT_USER),       @Data.value('(/EVENT_INSTANCE/EventType)[1]', 'nvarchar(100)'),       @Data.value('(/EVENT_INSTANCE/TSQLCommand)[1]', 'nvarchar(2000)') ) ;  GO

 

Code Walthrough

First, we declare a variable named @Data that will be of XML data type

Next, we assign the value returned by the EventData() function to the variable

Then, in the INSERT statement, we retrieve the element values in the @Data variable using XQuery and the value() method. We use the value() method as it takes a second parameter, represented by the value 1 as it is based on the zero index, that is the name of one of the SQL Server built-in data types. The value is returned as an instance of that type. Also, the value() method gives you better results with the formatting of the XML data

Test the trigger

Let's add a new column on the Region table in the Northwind database

USE Northwind   GO   ALTER TABLE Region  ADD newColumn SMALLDATETIME NULL

Querying the EvtLog table will give you the data returned by the EventData() function, stored in tabular format as we have already extracted the element values inside the XML data from inside our trigger definition.

 

Source collected from mssqltips.com