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If you ve never used SQL before, you may want to play around with it and create some sample queries before you start using it in an ASP.NET site. Most database products provide some sort of tool for testing queries. If you re using a full version of SQL Server, you can try SQL Server Management Studio or SQL Query Analyzer. If you don t want to use an extra tool, you can run your queries using the Server Explorer window described earlier. Just follow these steps in Visual Studio: 1. Right-click your connection, and choose New Query. 2. Choose the table (or tables) you want to use in your query from the Add Table dialog box (as shown in Figure 15-5), click Add, and then click Close.

Note This example shows how ADO.NET works to retrieve a simple result set. Of course, ADO.NET also

provides handy controls that go beyond this generic level and let you provide full-featured grids with sorting and editing. These controls are described in 15 and 16. For now, you should concentrate on understanding the fundamentals about ADO.NET and how it works with data.

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3. You ll now see a handy query-building window. You can create your query by adding check marks next to the fields you want, or you can edit the SQL by hand in the lower portion of the window. Best of all, if you edit the SQL directly, you can type in anything you don t need to stick to the tables you selected in step 2, and you don t need to restrict yourself to Select statements. 4. When you re ready to run the query, select Query Designer Execute SQL from the menu. Assuming your query doesn t have any errors, you ll get one of two results. If you re selecting records, the results will appear at the bottom of the window (see Figure 15-6). If you re deleting or updating records, a message box will appear informing you how many records were affected.

of objects, be sure that you ve also checked for the proper ownership. All for..in loops should contain an object.hasOwnProperty() check so that inherited properties are not unexpectedly encountered.

Now that you understand how to retrieve data, it isn t much more complicated to perform simple insert, update, and delete operations. Once again, you use the Command object, but this time you don t need a DataReader because no results will be retrieved. You also don t use a SQL Select command. Instead, you use one of three new SQL commands: Update, Insert, or Delete. To execute an Update, Insert, or Delete statement, you need to create a Command object. You can then execute the command with the ExecuteNonQuery() method. This method returns the number of rows that were affected, which allows you to check your assumptions. For example, if you attempt to update or delete a record and are informed that no records were affected, you probably have an error in your Where clause that is preventing any records from being selected. (If, on the other hand, your SQL command has a syntax error or attempts to retrieve information from a nonexistent table, an exception will occur.)

Tip When programming with ADO.NET, it always helps to know your database. If you have information on hand about the data types it uses, the stored procedures it provides, and the user account you need to use, you ll be able to work more quickly and with less chance of error.

Before you can update and insert records, you need to make a change to the previous example. Instead of displaying the field values in a single, fixed label, you need to show each detail in a separate text box. Figure 14-12 shows the revamped page. It includes two new buttons that allow you to update the record (Update) or delete it (Delete), and two more that allow you to begin creating a new record (Create New) and then insert it (Insert New).

To retrieve one or more rows of data, you use a Select statement. A basic Select statement has the following structure:

Figure 14-12. A more advanced author manager The record selection code is identical from an ADO.NET perspective, but it now uses the individual text boxes: protected void lstAuthor_SelectedIndexChanged(Object sender, EventArgs e) { // Define ADO.NET objects. string selectSQL; selectSQL = "SELECT * FROM Authors "; selectSQL += "WHERE au_id='" + lstAuthor.SelectedItem.Value + "'"; SqlConnection con = new SqlConnection(connectionString); SqlCommand cmd = new SqlCommand(selectSQL, con); SqlDataReader reader; // Try to open database and read information. try { con.Open();

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