Tài liệu Retrieve Results from SQL Server by Using the DataTable Object docx

3.2 Retrieve Results from SQL Server by Using the DataTable Object

The data reader is great when you just want to load data into a ListBox or ComboBox

control manually, but you can save some coding by binding the ListBox control to a data

table at runtime, as well as providing the ability to get not only the displayed value, but

the key column as well. This How-To demonstrates how to bind a limited ListBox

control to a data table.

Although getting the quick information is great, you need to be able to refer back to the

table of information, and you don't want to have to open another connection to get there.

You know that the DataTable object should allow you to perform this task. How do you

get results from SQL Server by using the DataTable object?

Technique

Using the Windows Forms controls that were introduced in How-To 3.1, you will use a

familiar object from Chapter 1 called the DataAdapter object. This time, instead of using

the OleDbDataAdapter data control, you will use the OleDbDataAdapter class from the

System.Data.OleDb Namespace.

Using a similar technique that was used when filling a DataSet, you will instantiate the

data adapter by assigning the SQL string and connection object. Then, instead of filling a

DataSet object, you will fill a DataTable object. Because you will only be dealing with a

table's worth of data, you just need to use a data table. That way, you will be able to

perform lookups more conveniently, as shown in the next How-To.

For now, the next step will be to assign the following properties of the list box:

• DataSource. This will be set to the DataTable object-in this case, dtCust.

• DisplayMember. This specifies which column from the data table to use for

display in the list box.

• ValueMember. Here, you will specify which column you want to use for the value

that is retrieved when an item is selected from the list box.

By programming the ListBox control using this technique, you can access the

ValueMember column in the SelectItem property of the list box.

Steps

Open and run the VB.NET-Chapter 3 solution. From the main form, click on the

command button with the caption How-To 3.2. When the form loads, click on the Load

List command button. You will see the list below fill with all the company names that

start with A.