注意，ProductsTableAdapters类从Products表中返回的是CategoryID和SupplierID的值，但并不包括Categories表 的CategoryName字段和Suppliers表的CompanyName字段，尽管当我们显示产品信息时，这些很可能是我们想要显示的字段。我们可以扩充TableAdapter的起始方法GetProducts()来包含CategoryName和CompanyName字段的值，这方法进而会更新强类型的DataTable来包括这些新的字段。
但这会造成一个问题，因为TableAdapter的插入，更新，删除数据的方法是基于这个起始方法的，幸运的是，自动生成的插入，更新，删除方法并不会受SELECT子句中的子查询的影响。如果我们注意把对Categories和Suppliers的查询添加成子查询，而不是用JOIN语 句的话，我们可以避免重做这些修改数据的方法。在ProductsTableAdapter中的GetProducts()方法上按右鼠标，选择“配置”，然后，把SELECT子句改成：
SQL
SELECT ProductID, ProductName, SupplierID, CategoryID,
QuantityPerUnit, UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued,
(SELECT CategoryName
FROM Categories
WHERE Categories.CategoryID = Products.CategoryID) as CategoryName,
(SELECT CompanyName
FROM Suppliers
WHERE Suppliers.SupplierID = Products.SupplierID) as SupplierName
FROM Products
图29: 更新GetProducts()方法的SELECT语句
在更新GetProducts()方法使用这个新查询语句之后，对应的DataTable将包含2个新字段，CategoryName和SupplierName。
图30: Products DataTable多了2个新字段
花点时间把GetProductsByCategoryID(categoryID)方法中的SELECT 子句也更新一下。
如果你使用JOIN句法更新GetProducts()中的SELECT语句的话 ，DataSet设计器不能使用DB直接模式自动生成插入，更新，以及删除数据库记录的方法。你必须手工生成这 些方法，就象本教程早先时候我们对InsertProduct方法的做法一样。此外，你必须手工提供InsertCommand，UpdateCommand和DeleteCommand属性值，假如你想使用批更新模式的话。
完成数据访问层：添加其他的TableAdapter
到目前为止，我们只讨论了针对单个数据表的单个TableAdapter。但是，Northwind数据库里含有我们需要在我们的web应用中使用的几个相关的表。一个强类型的DataSet可以包含多个相关的DataTable。因此，为了完成我们的DAL，我们需要为这些我们将来要用到的数据表添加相应的DataTable。步骤如下，打开 DataSet设计 器，在设计器上按右鼠标，选择“添加/TableAdapter”。这会生成一个新的DataTable和TableAdapter，然后我们早先讨论过的配置向导会指引你完成配置。
花上几分钟，创建对应于下列查询的TableAdapter及其方法。注意，ProductsTableAdapter的查询中包含了用以获取每个产品的分类和供应商名字的子查询。另外，如果你是随着教程在做的话，你已经添加过ProductsTableAdapter类的GetProducts()和GetProductsByCategoryID(categoryID)方法了。
ProductsTableAdapter GetProducts:
SELECT ProductID, ProductName, SupplierID, CategoryID,
QuantityPerUnit, UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued ,
(SELECT CategoryName
FROM Categories
WHERE Categories.CategoryID = Products.ProductID) as CategoryName,
(SELECT CompanyName
FROM Suppliers
WHERE Suppliers.SupplierID = Products.SupplierID)
as SupplierName
FROM Products GetProductsByCategoryID:
SELECT ProductID, ProductName, SupplierID, CategoryID,
QuantityPerUnit, UnitPrice, UnitsInStock, UnitsOnOrder,
ReorderLevel, Discontinued ,
(SELECT CategoryName
FROM Categories
WHERE Categories.CategoryID = Products.ProductID) as CategoryName,
(SELECT CompanyName
FROM Suppliers
WHERE Suppliers.SupplierID = Products.SupplierID) as SupplierName
FROM Products
WHERE CategoryID = @CategoryID GetProductsBySupplierID
SELECT ProductID, ProductName, SupplierID, CategoryID, QuantityPerUnit, UnitPrice,
UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued ,
(SELECT CategoryName
FROM Categories
WHERE Categories.CategoryID = Products.ProductID) as CategoryName,
(SELECT CompanyName FROM Suppliers
WHERE Suppliers.SupplierID = Products.SupplierID) as SupplierName
FROM Products
WHERE SupplierID = @SupplierID GetProductByProductID
SELECT ProductID, ProductName, SupplierID, CategoryID, QuantityPerUnit,
UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued ,
(SELECT CategoryName
FROM Categories
WHERE Categories.CategoryID = Products.ProductID) as CategoryName,
(SELECT CompanyName
FROM Suppliers
WHERE Suppliers.SupplierID = Products.SupplierID) as SupplierName
FROM Products
WHERE ProductID = @ProductID CategoriesTableAdapter GetCategories
SELECT CategoryID, CategoryName, Description
FROM Categories GetCategoryByCategoryID
SELECT CategoryID, CategoryName, Description
FROM Categories
WHERE CategoryID = @CategoryID
SuppliersTableAdapter GetSuppliers
SELECT SupplierID, CompanyName, Address, City, Country, Phone
FROM Suppliers GetSuppliersByCountry SELECT SupplierID, CompanyName, Address,
City, Country, Phone
FROM Suppliers
WHERE Country = @Country GetSupplierBySupplierID
SELECT SupplierID, CompanyName, Address, City, Country, Phone
FROM Suppliers
WHERE SupplierID = @SupplierID EmployeesTableAdapter GetEmployees
SELECT EmployeeID, LastName, FirstName, Title, HireDate, ReportsTo, Country
FROM Employees GetEmployeesByManager
SELECT EmployeeID, LastName, FirstName, Title, HireDate, ReportsTo, Country
FROM Employees
WHERE ReportsTo = @ManagerID GetEmployeeByEmployeeID
SELECT EmployeeID, LastName, FirstName, Title, HireDate, ReportsTo, Country
FROM Employees
WHERE EmployeeID = @EmployeeID
图31:完成数据访问层：添加了四个TableAdapter后的DataSet设计器