Tài liệu Creating a Connection Object Using Visual Studio .NET pdf

Creating a Connection Object Using Visual Studio .NET To create a SqlConnection object using Visual Studio .NET, you drag a SqlConnection object from the Data tab of the Toolbox to your

Creating a Connection Object Using Visual Studio NET

To create a SqlConnection object using Visual Studio NET, you drag a SqlConnection object from the Data tab of the Toolbox to your form You'll recall that a SqlConnection object allows you to connect to a SQL Server database You can also drag an

OleDbConnection object from the Toolbox to your form to connect to a database that supports OLE DB

name of sqlConnection1

Figure 7.1: Creating a SqlConnection object with Visual Studio NET

Once you've created a SqlConnection object, that object appears in the "tray" below the form The tray is used to store nonvisual components like SqlConnection objects Other objects that appear in the tray are SqlCommand objects These objects are considered nonvisual because you don't see them when you run your form You can of course still work with them visually when designing your form

To the right of the form, you'll notice the Properties window, which you use to set the properties for your SqlConnection object To set the ConnectionString property that specifies the details of the database connection, you can either type in the string directly

or click the drop-down list and build the ConnectionString visually To do this, you select New Connection from the drop-down list, which displays the Data Link Properties dialog box This dialog box contains four tabs, the first of which is the Provider tab, which

Figure 7.2: Selecting the provider

Click the Next button to continue to the Connection tab (you can also click the

Connection tab directly), where you enter the details for your database connection, as

Figure 7.3: Entering the connection details

Warning For security reasons, do not enable the Allow Saving Password check box If

you did, your password would be stored in the actual code, and anyone could get your password from the code Leave Allow Saving Password in its default non-enabled state; that way, the user will be prompted to enter the password For testing purposes, however, leaving your password in is sometimes

acceptable-just remember not to release your password in production code Once you've entered your connection details, you can press the Test Connection button to ensure your details are correct

At this point, you've entered all the mandatory details, and you can choose to save your details by clicking OK, or you can click Advanced to enter additional details such as the

Figure 7.4: Entering the advanced connection details

You can also click the All tab to view and edit all the values for the connection, as shown

in Figure 7.5 To edit a value, you click Edit Value

Figure 7.5: Viewing all the connection details

Click the OK button to save your connection details

On my computer, the ConnectionString property for my SqlConnection object that connects to the SQL Server Northwind database is set to

data source=localhost;initial catalog=Northwind;persist security info=False;

user id=sa;pwd=sa;workstation id=JMPRICE-DT1;packet size=4096

Note The persist security info Boolean value controls whether security-sensitive

information such as your password is returned in a connection that has been

previously opened You'll typically want to leave this in the default setting of False.

Coding an Event in VS NET

You can add code for an event in VS NET For example, let's say you wanted to add code for the State-Change event of the sqlConnection1 object created earlier To do this, you first select sqlConnection1 in the tray, then you click the Events (lighting) button in

Figure 7.6: sqlConnection1 object's events

You then double-click the name of the event in the Properties window you want to code

In this example, you double-click the StateChange event VS NET then displays the code

cursor shows where you add your code

Figure 7.7: The beginning StateChange event handler method

All you have to do is add your code to the event handler method For example, you can set your method to

private void sqlConnection1_StateChange(

object sender, System.Data.StateChangeEventArgs e)

{

Console.WriteLine(

"State has changed from "+

e.OriginalState + "to "+

e.CurrentState

);

}

Figure 7.8: The completed StateChange event handler method

Once you've created a SqlConnection object, you can then use it with other ADO.NET objects, such as a SqlCommand object You'll see how to do that with VS NET in

Chapter 8