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).
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")
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
objTask.Name = TaskName
objSQLServer.Executive.Tasks.Add objTask
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 that 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 SQLServer object:
objSQLServer.Connect Server, UserID, Password
Note that 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 the 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 following 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 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.
