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Data Management Objects: Collections and the Database Object

Last updated Mar 28, 2003.

In previous SQL-DMO programming articles, I covered the basics of accessing SQL Server via a programming library. I explained the properties and methods you can use on the SQL Server object, and then created a small program to request some information to connect to a server and potentially shut down the SQL Service on that system.

We've used VBScript, although other (more powerful) languages can also be used, and the only tools we've pressed into service are Notepad and the SQL-DMO libraries. But you have many options. You might want to use a more powerful Integrated Development Environment (IDE), such as Visual Studio to provide context-sensitive drop down object references and color-coded syntax checking. Several editors are available for VBScript, and you can also download VB.NET Express, for free. (At the end of this article I provide links to these products.)

NOTE

For other languages, references or includes may be necessary to access the SQL-DMO library.

As I mentioned in my last installment, I'll keep the code for each article separate. To create a centralized tool for your own purposes, you can combine these code segments in Web pages, C# programs, and the like. If you do that, you only have to create the server object, connect to it and clean up, one time. That depends, of course, on what you do in the code. It's not uncommon to have to have more than one server object to perform certain activities. I'll try to make you aware of those situations as we go along.

In this article, we create and use the next object in the SQL-DMO library: the database object. To access this object, we reference the SQL-DMO library, create and logon to a server, and then create and use the database object. This object has the same behavior as the server object, with different properties and methods.

Collecting Our Thoughts

At this point, we need to talk about collections. We started with the SQLServer object, but even this object isn't the highest level in the SQL-DMO library. A SQL Server (like our refrigerator example) is part of a group, called SQL Servers. This grouping is called a collection. Collections have properties and methods as well as the objects they contain.

Within the collection, there are objects of a kind. This means that the Databases collection contains all of the databases on a server, the Tables collection within a database contains all of the tables in a database, and so forth. Once you reference the collection, you have a list of items of that type that you can work with.

Let's take a look at some code for the database collection and then break down each section. Along the way, you'll learn about various aspects of collections and database objects.

TIP

As before, you can copy-and-paste this code into a notepad, save it with the extension ".vbs" and run it on your personal development environment.

' dmoListDatabases.vbs
' Created: 	12/24/04 - Buck Woody
' Change Log:	

' Variable to hold Server Name
Dim ServerNameVar
' Variables for the text boxes
Dim ServerDisplayVar
Dim MsgTxtVar
' Variables for objects
Dim oServer
Dim oDatabase

' Ask for the name
ServerNameVar = InputBox("Enter Server Name:")
	If ServerNameVar = "" Then
		ServerNameVar = "(local)"
	End If

' Create the server object using SQL-DMO
Set oServer = CreateObject("SQLDMO.SQLServer2")
' Login with current Windows account
oServer.LoginSecure = True
oServer.Connect ServerNameVar

' Fill the variable with database names
For each oDatabase in oServer.Databases
MsgTxtVar = MsgTxtVar & VbCRLf _
	& oDatabase.Size & " MB " & Chr(9) & oDatabase.Name 
Next

' Get the message box
ServerDisplayVar = MsgBox(MsgTxtVar, VBOK, "Databases on " & ServerNameVar)

' Clean up
set oDatabase = Nothing
Set oServer = Nothing

If you've followed along with the last two articles, you might have caught an error in the earlier code. It's a particularly insidious error, because it allows the code to work anyway, so it's sort of hidden. Here's the problem section in the previous code:

...
' Ask for the name
ServerNameVar = InputBox("Enter Server Name:")
	If ServerNameVar = "" Then
		ServerName = "(local)"
	End If
...

Do you see it? The line with "(local)" would never run, since ServerName isn't a variable that's used anywhere. With Visual Basic or any of the .NET languages, this would have thrown an error because the ServerName variable was never declared. VBScript has no problem with it, because it doesn't always require variables to be declared. It just created a new one (called ServerName) that is just never used.

So why did the program work? It would seem that the connection command should have failed in the line that reads:

...
oServer.Connect ServerNameVar
...

The reason the code still works has to do with the default behavior of SQL Server. If no server name is specified in most SQL Server tools (including, it seems, in SQL-DMO), then the name defaults to (local). While this behavior didn't cause us any issues here, it certainly could do so down the road. We might want to display the name of the variable, and nothing would show up. As you can see, I've caught the error and set the variable name correctly.

In addition I created two new variables for this exercise: oServer and oDatabase. Just as before, these aren't strictly necessary, but it's good programming practice to spell out all variables.

The next few lines are just as we've seen them before, creating a server object and connecting to it.

After the connection is made, the following code does the work:

' Fill the variable with database names
For each oDatabase in oServer.Databases
MsgTxtVar = MsgTxtVar & VbCRLf _
	& oDatabase.Size & " MB " & Chr(9) & oDatabase.Name 
Next

A few things are happening here, so let's take a look at each line.

The For each statement begins a loop. It takes each item in a set, and begins to process them; stopping after it runs out of items to work on. The Next statement makes it recognize the end of the block and move on to the next member in the set. I've told the code to look for each of the Database objects in the collection of databases on the oServer object with the in qualifier.

On the next line, I take the MsgTextVar variable and fill it with the items in the list. Notice that I set it equal to itself, first. If you follow the processing logic for the statement, it becomes clear as to why I might do this. If I change that line to this:

MsgTxtVar = oDatabase.Size & " MB " & Chr(9) & oDatabase.Name

Each time the line iterates through the set, the entire variable would be reset to the current value; I would end up with one entry in the variable. Setting the variable to itself in each iteration adds that variable to what was already there. Notice that I include the VbCRLF to the code so that I get a hard return.

Now that I have access the databases collection, I can reference the individual database and begin to get properties on it, just as I did on the server objects in the previous articles. The first property I go after is the .Size property, which displays the size of the database data and indexes in Megabytes. I include the MB designation to make sure the units are clear to the user.

On that same line is a bit of formatting; the Chr(9) stands for ASCII character 9, which is the Tab key. You could also use another constant, VBTab, to make this more readable.

Finally I end up with the .Name property. This property displays the name of the database.

At the end of the program, I clean up the objects that I've created to release the memory and other resources they consume.

In this example, as in the previous iterations, I send the output to a message box. You can combine these sections of code to create tables in a Web page, logging files on the hard drive, or messages sent through e-mail. You can create reports or lists, or store the output in another database. In future articles, I'll explain how to send T-SQL commands using the SQL-DMO libraries, and you can use the return values you've learned so far in those queries as well.

Online Resources

The full documentation for the Server Object Library can be found here.

Want to learn more about scripting? About.com has a good treatment for code outside of SQL-DMO.

Want a full .NET language IDE for free? Check here.

InformIT Tutorials and Sample Chapters

Sharon Dooley discusses SQL-DMO in her book, SQL Server 7 Essential Reference that you can read right here on Safari.