Entity Framework学习初级篇5--ObjectQuery查询及方法

作者佚名技术来源 NET编程浏览发布时间 2012-05-22

{

string esql　= "select value c.City from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

ObjectQuery<string> query = edm.CreateQuery<string>(esql　);

query = query.Distinct();

foreach (string c in query)

{

Console.WriteLine("City {0}", c);

}

}

l　Except:返回两个查询的差集。实例代码如下：

using (var edm = new NorthwindEntities()) { string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10"; ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1); string esql2 = "select value c from NorthwindEntities.Customers as c where c.Country=''UK'' order by c.CustomerID limit 10"; ObjectQuery<Customers> query2 = edm.CreateQuery<Customers>(esql2); query1 = query1.Except(query2); foreach (Customers c in query1) { Console.WriteLine(c.Country); //输出:UK } }

l　Intersect：返回两个查询的交集。实例代码如下：

using (var edm = new NorthwindEntities()) { string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10"; ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1); string esql2 = "select value c from NorthwindEntities.Customers as c where c.Country=''UK'' order by c.CustomerID limit 10"; ObjectQuery<Customers> query2 = edm.CreateQuery<Customers>(esql2); query1 = query1.Intersect(query2); foreach (Customers c in query1) { Console.WriteLine(c.Country); } }

l　Union/UnionAll　:返回两个查询的合集，包括重复项。其中UnionAll必须是相同类型或者是可以相互转换的。

l　Include:可通过此方法查询出与相关的实体对象。实例代码如下：

using (var edm = new NorthwindEntities()) { string esql1 = "select value c from NorthwindEntities.Customers as c WHERE c.CustomerID =''HANAR''"; ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1); query1 = query1.Include("Orders"); foreach (Customers c in query1) { Console.WriteLine("{0},{1}", c.CustomerID, c.Orders.Count); //输出：HANAR,14 } }

l　OfType：根据制定类筛选元素创建一个新的类型。此类型是要在实体模型中已定义过的。

l　OrderBy

实例代码如下：

using (var edm = new NorthwindEntities()) { string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10"; ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1); query1.OrderBy("it.country asc,it.city asc"); //也可以这样写 //query1.OrderBy("it.country asc"); //query1.OrderBy("it.city asc"); foreach (Customers c in query1) { Console.WriteLine("{0},{1}", c.Country, c.City); } }

l　Select

实例代码如下：

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