Visual Studio 2008之语言特性 查询语法.docVIP

Visual Studio 2008之语言特性 查询语法 2007-11-14 10:02作者：韩现龙的博客出处：天极网软件频道责任编辑：幽灵 　　If instead of returning Person objects, I wanted to return just the firstnames of the people in the collection, I could re-write my query like so: 　　如果我不返回一个Person对象，只想返回collectioin中所有人的名字的集合，可以按照如下方式重写该查询语句： 　　 　　Note above how I am no longer saying select p, but am instead saying select p.FirstName. This indicates that I dont want to return back a sequence of Person objects - but rather I want to return a sequence of strings - populated from each Person objects FirstName property (which is a string). The datatype result of this query syntax expression is consequently of type IEnumerable. 　　注意上边我没再用“select p，而是用select p.FirstName。这表明我不想让查询返回Person对象，而是想返回一个字符串--这个字符串是Person这个对象的FirstName属性(是个字符串)中取得的。因此，该查询表达式返回值的数据类型是IEnumerable。 　　Sample Query Syntax Against a Database 　　关于对数据库查询的事例： 　　The beauty of LINQ is that I can use the exact same query syntax against any type of data. For example, I could use the new LINQ to SQL object relational mapper (ORM) support provided in Orcas to model the SQL Northwind database with classes like below (please watch my video here to learn how to-do this): 　　LINQ的美在于我可以对任何类型的数据使用完全一致的查询语法。比如，我可以用在Orcas中提供的新的LINQ to SQL ORM来构建SQL 的Northwind数据库，如下图：((请看我的视频来学习如何做：watch my video here )： 　　 　　Once Ive defined the class model above (and its mapping to/from the database), I can then write a query syntax expression to fetch all products whose unitprice is greater than $99: 　　一旦我定义了如上的类模型(和它的 从/向 数据库中绘制出来的图)，我可以写一个查询语句，查找出unitprice比99$多的产品来： 　　 　　In the above code snippet I am indicating that I want to perform a LINQ query against the Products table on the NorthwindDataContext class created by the ORM designer in Visual Studio Orcas. The select p indicates that I want to return a sequence of Product objects that match my query. The datatype result of this query syntax expression is consequently of type IEnumerable. 　　在上边的代码片断中，我指明了我想对用ORM设计器生成的NorthwindDataContext类的Pr