Creating a Parameterized Query
I've been asked by a couple readers on how to pass parameters into a SQL statement to your database using the TableAdapters. I actually created a video on how to do this in the context of a search query (play video | download video | entire series). It's really easy to do this using the TableAdapter Query Configuration Wizard. Let's create a quick login form for an example.
I've got a table called Users in my database and I've created a Dataset called UsersDataset by opening up the Datasources window and adding a new datasource to my database. Then I created a form called LoginForm and from the Toolbox I dragged some labels and textboxes for the entry and a couple buttons, OK and Cancel, onto the form. I then set the PasswordChar property on the PasswordTextbox to "*". This indicates that the textbox should display this character instead of what the user types, but the value of the Text property will still be what the user enters.
(By the way, this example does NOT demonstrate a secure way of writing login forms. We'll be passing what the user enters directly into the database which stores the password in clear text. It is NOT safe practice to store clear text passwords in your database. I'll post a follow-up that talks about techniques we can use to protect users' passwords, especially if we need to store them in a database. For now, let's concentrate on how we add parameterized queries to our TableAdapters. UPDATE: Here's the follow up.)
Now at this point I build the project and in the WindowsApplication1 Components section at the top of the Toolbox I can now see the UsersDataset and the UsersTableAdapter listed (it's important that you build your project to get the components listed in the Toolbox). I drag the UsersTableAdapter onto the LoginForm which creates a component in the tray named UsersTableAdapter1.
So now that we've got that all set up, we're going to add a parameterized query to the UsersTableAdapter. First open up the UsersDataset and right-click on the TableAdapter in the designer and choose "Add Query".
This will open up the TableAdapter Query Configuration Wizard. First it asks you to choose a command type. Keep the default selected as "Use SQL Statement" and then click Next. Next it asks you to choose a query type. We're going to select the second option, to create a SELECT statement that returns a single value, not a result set.
Next we'll write the parameterized query as "SELECT COUNT(*) FROM Users WHERE UserName = @UserName AND Password = @Password". Then click Next and name the function "Login". This will create a TableAdapter method called Login that accepts a UserName and Password as a parameter and returns an Object which will be an Integer in our case since we're specifying to return the COUNT(*) of the rows that match the WHERE clause.
Now back to the LoginForm, we can double-click on the OK button to add a Click event handler.
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
Handles Button1.Click
Try
If CType(Me.UsersTableAdapter1.Login(Me.UserNameTextBox.Text, _
Me.PasswordTextBox.Text), Integer) > 0 Then
MsgBox("Welcome to my application!")
Else
MsgBox("Invalid username or password.")
End If
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Sub
Now when we run this example and enter a user name and password that is contained in the database table Users, we get the greeting message otherwise we get the message that our user name or password is invalid.
As you can see it's really easy to add parameterized queries to your TableAdapters using the wizards. There's even a simple query builder you can use to help you write your queries and test them out before they are generated on the TableAdapter. In a follow up post I'll show you how to add secure password storage to your application using hashing and encryption.
Beth is a Program Manager on the Visual Studio Community Team at Microsoft and is responsible for producing and managing content for business application developers, driving community features and team participation onto MSDN Developer Centers (http://msdn.com), and helping make Visual Studio one of the best developer tools in the world. She also produces regular content on her blog (http://blogs.msdn.com/bethmassi), Channel 9, and a variety of other developer sites and magazines. As a community champion and a long-time member of the Microsoft developer community she also helps with the San Francisco East Bay .NET user group and is a frequent speaker at various software development events. Before Microsoft, she was a Senior Architect at a health care software product company and a Microsoft Solutions Architect MVP. Over the last decade she has worked on distributed applications and frameworks, web and Windows-based applications using Microsoft development tools in a variety of businesses. She loves teaching, hiking, mountain biking, and driving really fast.
