Saving and Retrieving Data with AJAX - Pay No Attention to That Man Behind the Curtain
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When you’ve completed the table setup, click Next, to move to the last page of the Wizard, and then click the Test Query button. The test fails, as shown in Figure 4-9.
Figure 4-9. The Wizard let you down; the Query Test failed and you’re looking at this error message because this database requires a schema name in front of the table names.
In this instance, the Wizard falls on its face. It turns out that the AdventureWorks database prefixes a schema name in front of each table name and the Wizard is unprepared for that. It generates a SELECT statement without schema names, as you saw back in Figure 4-8.
Schema in this context refers to an optional name used for organizing the tables in a large database. For example, in the AdventureWorks database, all the tables relating to the HR department have the schema name HumanResources prefixed to every table name, separated by a period, such as HumanResources.EmployeeAddress. Other schemas in the AdventureWorks database include Person, Production, Purchasing, and Sales.
As mentioned, a schema name is optional in SQL. In fact, in our experience, they are rarely used, and the Wizard is unaware of them. However, since the AdventureWorks database (which ships as part of Microsoft SQL Server) does use them, the Wizard becomes confused and flies off to Kansas leaving you on your own.
The square brackets surrounding each field and table name in the generated SELECT statement are not required, but are used to guarantee that there will be no problems if the name includes any space characters (usually a very bad idea in any case). We often remove them from the finished statement to enhance readability.
Think of this as proof that people are not yet entirely replaceable by automation. Hit the Previous button to go back one step and fix the SELECT statement manually. Click the radio button captioned “Specify a custom SQL statement or stored procedure,” and then click Next. In the SQL Statement box, shown in Figure 4-10, type in:
SELECT ProductID, Name, ProductNumber, MakeFlag, SafetyStockLevel, ReorderPoint
FROM Production.Product
Figure 4-10. The SQL statement editing dialog, after adding the schema name to the table name,
and removing all the extraneous square brackets.
As you can see, this is nearly the same SELECT statement that you built with the Wizard in Figure 4-8, except the Product table now has the required schema (Production) in front of it. We’ve also left out the square brackets on the columns, as mentioned in the note above.
Click Next to proceed to the next page of the Wizard, and then click Test Query. This time, you should get the results shown in Figure 4-11.
Figure 4-11. When you test the SELECT statement this time, you’ll see the results you were looking
for.
Behold—the triumph of 3 billion years of random mutation and natural selection over 50 years of automation!
Click Finish to save your work. It may not look like much, but you’ve just enabled your application to access the AdventureWorks database, meaning all that data is now at your control.
Please check back next week for the continuation of this article.
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 This article is excerpted from chapter four of Learning ASP.NET 2.0 with AJAX: A Practical Hands-on Guide, written by Jesse Liberty, Dan Hurwitz and Brian MacDonald (O'Reilly, 2007; ISBN: 0596513976). Check it out today at your favorite bookstore. Buy this book now.
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