Friday, August 26, 2005

Creating a DML trigger using CLR in SQL Server 2005

In this article, we will take a look at the new CLR integration feature and learn how to create triggers in SQL Server using a managed code. We would create a simple DML delete trigger for a table and access the deleted value from our C# code.

Visual Studio .NET 2005

1. Open a C# -- Database project
2. Create a new trigger file into it.
3. The .NET class that will implement the functionalities of the trigger is given below just copy-paste it into the new file.

GetTriggerContext() :: Get reference to the current trigger context by invoking this method of the SqlContext class. This help us in fetching the data from the virtual table which would be created during a execution of a trigger.

using System;
using System.Data;
using System.Data.Sql;
using System.Data.SqlServer;
using System.Data.SqlTypes;

public partial class Triggers
{
// Enter existing table or view for the target and uncomment the attribute line
// [SqlTrigger (Name="SampleCLRTrigger", Target="EmployeeInfo", Event="FOR Delete")]
public static void SampleCLRTrigger()
{
SqlTriggerContext triggerContext = SqlContext.GetTriggerContext();
SqlPipe sqlPipe = SqlContext.GetPipe();
SqlCommand command = SqlContext.GetCommand();

if (triggerContext.TriggerAction == TriggerAction.Delete)
{
command.CommandText = "Select * from Deleted";
sqlPipe.Execute(command);
}
}
}

Build and compile the .NET class to create a .NET assembly out of it. In VS.NET 2005 it is as simple as Ctrl+Shift+B. The DLL would have been created in the BIN directory. From the properties of that DLL get to know the path of the created DLL.

SQL Server 2005

Then open SQL Server Management Studio and create a new query. Register the assembly in SQL Server using the below code snippet.

Create Assembly assTestCLRTrig
FROM 'C:\Documents and Settings\Administrator\My Documents\Visual Studio\Projects\SqlServerProject1\SqlServerProject1\bin\Debug\SqlServerProject1.dll'

Script to create a table for demo purpose:

Create table EmployeeInfo
(
EmpId int identity(1,1),
EmpName varchar(50),
EmpAddr varchar(100),
EmpContactNo varchar(20)
)

Insert a sample record

Insert into employeeinfo values ('vadi','address comes here','5201')

Script to create a trigger

Create trigger trgDeleteEmployeeInfo
On
EmployeeInfo
For Delete
As External Name
assTestCLRTrig.Triggers.SampleCLRTrigger

The syntax used above for External Name is "AssemblyName.NameOfTheClass.MethodName"

By default execution of the code in .NET framework is disable ... so just run the below two lines to enable it.

sp_configure 'clr enabled', 1
Reconfigure with override

Lets test our work:

Delete from employeeinfo where empid=1

It would display the record deleted in a tabular fashion. So far, we have seen the steps involved in creating the trigger and executing that trigger from Yukon .. hope it was useful to you!

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