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ASP AND SQL-DMO Create a Server Component


March 25,2004
15 Seconds : ASP AND SQL-DMO:Create a Server Component Encompassing the SQL-DMO Functionality
S.S. Ahmed
10/30 /2000

Introduction

Before starting, let's shed some light on the SQL Distributed Management Objects (SQL-DMO). ASP gets its
functionality by using server components. In ASP we can combine scripts, HTML, and reusable server
components to create scalable Web applications. These server-side ActiveX components can be developed in
many languages, such as VC++, Java, and Visual Basic (VB).


click here to download source code used in this article
ftp://ftp.15seconds.com/001031.zip

I have selected VB to develop a component that will be used in ASP scripts to harness the power of SQL-
DMO. SQL-DMOs are OLE automation-compatible COM objects. These objects and a set of properties and methods
are used to write programs to administer multiple SQL Servers distributed across a network. Also, SQL-DMO
is the foundation of SQL Enterprise Manager. In fact, SQL-DMO is a very powerful object model of SQL
Server management. The obvious advantage of using a component encompassing SQL-DMO functionality is that
you can manage your SQL Server from anywhere in the world.

Although, SQL-DMO is a complete set of objects and methods to manage the SQL Server remotely, in this
article, we will only see how to add and remove SQL tasks in the Task Scheduler. I decided to write this
article because I couldn't find a good article about using SQL-DMO in ASP. The article, which details how
to leverage VB to create the ASP component, uses the following technologies:


Visual Basic 6
SQL Server


The Real Business

I have created a class named "Task." that contains all the code needed to implement the functionality.

This is the code from Task.cls:



Public Function AddTask()

...........................

    objSQLServer.DisConnect

    objSQLServer.Connect Server, UserID, Password

    Dim objTask As SQLOLE.Task
    Set objTask = CreateObject("SQLOLE.Task")

    'Set the schedule name
    objTask.Name = TaskName

    objSQLServer.Executive.Tasks.Add objTask

.................................

    Case "single_run":
    Case 2:

        If ExecutionDate = "" Then
            ErrDesc = "You must provide the task execution date."
            Exit Function
        Else
            If IsDate(ExecutionDate) = False Then
                ErrDesc = "Please provide a valid task execution date."
                Exit Function
            Else
                'Set the schedule name
                objTask.Name = TaskName

                objSQLServer.Executive.Tasks.Add objTask

                'Change the task!
                objTask.BeginAlter
                objTask.Database = DatabaseName
                objTask.Command = CommandText

                objTask.FrequencyType = SQLOLEFreq_OneTime
                objTask.ActiveStartDate = CDate(ExecutionDate)
                objTask.DoAlter
            End If
        End If

        If (objTask.CmdExecSuccessCode) Then
            ErrDesc = "Failure"
        Else
            ErrDesc = "Success"
        End If

End Function


The class has two main functions named AddTask and RemoveTask.AddTask adds a new task to the Scheduler.
Similarly, RemoveTask removes the task from the Scheduler. First of all, you will have to include
the "Microsoft SQL OLE Object library" from the references in the Project Menu. Once, you have done that,
follow the steps below:


Create a SQL Server object.
Connect to the SQL Server object.
Use the SQL Server object and other contained objects.
Release the SQL Server object.


Step 1

The following creates a new SQL Server object:



Dim objSQLServer As SQLOLE.SQLServer
Set objSQLServer = New SQLOLE.SQLServer


The objSQLServer object is an instance of the SQLOLE.SQLServer class. This object represents the SQL
Server in which tasks will be added or removed. It's needed in order to move ahead and create another
object that will be used to create a new task. Notice this uses the "New" keyword to instantiate the
SQLServer object. We could have used the CreateObject function instead, but late binding would have given
the app a slower performance. The reference through an early bound variable promotes a better performance.


Step 2

The following connects to the SQL Server object:



objSQLServer.Connect Server, UserID, Password


Note we have passed three arguments to the Connect method. The first argument is the name of the SQL
Server to which you want to connect, the second argument is the User ID required to log on to the SQL
Server, and thehe third argument is the password required to log on to the SQL Server. If you provide
correct parameters to the Connect method, you will be connected to the SQL Server.


Step 3

Once you are connected to the SQL Server, you can make use of the newly created object's methods and
properties to accomplish the task. Our task is to create a new task in the SQL Scheduler so we are going
to create a new task, and later we will set certain properties of this object.



Dim objTask As SQLOLE.Task
Set objTask = CreateObject("SQLOLE.Task")


Now that the task object has been created, we need to add the task to the scheduler. Define the task name
by calling the Name property of the Task object, and then add this task to the SQL Server Scheduler.



objTask.Name = TaskName
objSQLServer.Executive.Tasks.Add objTask


After the task has been added to the scheduler, it's time to add some commands in the newly created task.
You may want to create and run a task to delete particular records from a table at a particular time, or
you may want to send an email to the site administrator on an exact date of the month. All of this can be
done by assigning values to certain properties of the Task object. Look at the below statements:



objTask.BeginAlter
objTask.Database = DatabaseName
objTask.Command = CommandText

objTask.FrequencyType = SQLOLEFreq_OneTime
objTask.ActiveStartDate = CDate(ExecutionDate)
objTask.DoAlter


Before assigning values to the properties, you must call BeginAlter method, which tells the SQL Server
that changes are about to be made to the task properties. Actually, each change to a single property is a
separate update to SQL Server. We use the BeginAlter method to group multiple property changes into a
single unit. Call the DoAlter method to commit the changes made to the object properties. You can also
call the CancelAlter method to cancel the unit of property changes.

Assign a valid database name to the "Database" property. This is the database in which you want to execute
the task.



objTask.Database = DatabaseName


Pass a valid Transact SQL statement to execute for the task you have created to the "Command" property.



objTask.Command = CommandText


In the original Task code, we assigned a valid value to the FrequencyType property, which is the primary
frequency unit of time. More details are included in the source code files accompanying this article.
Please refer to the component's source code to see the different uses of the FrequencyType property.



objTask.FrequencyType = SQLOLEFreq_OneTime


The above line of code is meant to run only once, therefore a date is assigned to the ActiveStartDate
property. The task will automatically execute on this date. ActiveStartDate is the date before which this
task is active. There is another property which I think should be mentioned here, ActiveEndDate, the date
and time after which the task is active.



objTask.ActiveStartDate = CDate(ExecutionDate)


Using the code provided, you could create a task that would run on a daily basis, hourly basis, or only
once on the date provided as a parameter. By viewing the attached source code in Visual Basic, a reader
can see that it is thoroughly commented so the reader can understand the statements without frequently
pressing F1 to discover a statement's meaning. The following is the "RemoveTask" function that removes the
named task from the scheduler:



Public Function RemoveTask(ByVal Task As Variant)

..........................

    objSQLServer.Connect Server, UserID, Password

    objSQLServer.Executive.Tasks(CStr(Task)).Remove
    ErrDesc = "The task has been removed."

.........................

End Function


Remember, it's necessary to set certain properties before calling this method. Have a look at the
following statements:




Dim objTaskManager
Set objTaskManger = server.createobject("TaskManager.Task")

objTaskManager.Server = cstr(request.form("servername"))
objTaskManager.UserID = cstr(request.form("userid"))
objTaskManager.Password = cstr(request.form("password"))
objTaskManager.RemoveTask cstr(request.form("taskname"))

response.write objTaskManager.ErrDesc

Set objTaskManager = Nothing


This is the ASP code that shows how to instantiate the component and call the "RemoveTask" function.
Notice that before the function is called, server name, User ID, and Password values are passed to the
properties. Use the ErrDesc property to see the status of the function called.

Following is the ASP code needed to add a new task to the SQL Scheduler:



Dim objTaskManager
Set objTaskManager = server.createobject("TaskManager.Task")

objTaskManager.Server = cstr(request.form("servername"))
objTaskManager.UserID = cstr(request.form("userid"))
objTaskManager.Password = cstr(request.form("password"))
objTaskManager.DatabaseName = cstr(request.form("databasename"))
objTaskManager.TaskName = cstr(request.form("taskname"))
objTaskManager.CommandText = cstr(request.form("commandtext"))
objTaskManager.ScheduleType = cint(request.form("scheduletype"))
objTaskManager.ExecutionDate = cstr(request.form("executiondate"))
objTaskManager.AddTask

response.write objTaskManager.ErrDesc
Set objTaskManager = Nothing


The task created above will run only once because we have passed the current date to the ExecutionDate
property.


Compiling the Project

After entering the code in the class module, compile the project to make a DLL. It would be better to
reference the "Microsoft Active Server Pages Object Library" in the project so ASP will not give us
an "Out of Process Component" error message if we try to call the component from any ASP page. In a
nutshell, what this means is that this component will know that it needs to access the Active Server Pages
DLL (asp.dll) to run. Finally, compile the project as a DLL. Voila! You have created an ASP component that
can add and remove SQL Scheduler tasks.


Usage

Consider a scenario in which you create an e-commerce application. You have used SQL Server for data-
storage purposes. Users come and register on your site before doing any shopping on your site, and they
place orders, but leave your site without checking out.

You should be able to delete the items they placed in their shopping basket. It would be tedious to
manually check the database for valid records and delete the unwanted records. Instead, use the component
you just created and create a task that would search the database for invalid or unwanted records and
would delete them automatically after a certain amount of time.

Similarly, you can create and run a VB application once a month that would remove the accomplished tasks
from the SQL Server. Alternately, you could create a component that would check and remove the unwanted
tasks from the SQL Server, create a new task manually, and call this component using the extended stored
procedures provided with SQL Server to remove the unwanted tasks from the SQL Server. SQL Server 6.5 and
later provides the capability of loading and executing COM objects through a set of OLE Automation stored
procedures or through extended stored procedures.


Code Details

VB Component source code and ASP files to test the component are provided with this article. A compiled
DLL is also provided. Directly plug in the DLL in your Web application to test the component
functionality. Source code is also provided so that you can play with the code yourself and try to add
some more features in the component. ASP files are provided to test the component in ASP. Create and
remove tasks through these files. To run the ASP files, create a new Web application and include all the
ASP files in the new application, and open the index file, tm_demo1.asp, in your browser to test the
functionality.


Summary

Creating ASP Component to manage SQL Server remotely is fairly easy. It only requires a basic knowledge of
ASP, VB, and SQL Server. The article shows how easy it is to create a component that harnesses the power
of SQL-DMO and manages the SQL tasks remotely.

About the Author

S.S. Ahmed is a senior software engineer in a software development company that specializes in Web
application development. To contact Ahmed with questions or comments, email him at ss_ahmed1@hotmail.com.

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