ADO.Net Entity Framework Linq To Entities 语法功能汇编

Linq To Entities 的语法基础可以参考：

Microsoft Language Integrated Query (LINQ) 从入门到精通

1.使用ObjectQuery类的ToTraceString()方法显示查询SQL语句

             Console.WriteLine(customers.ToTraceString());

2.基于表达式的查询语法

    ObjectQuery<Customers> customers = edm.Customers;

    IQueryable<Customers> cust1 = from c in customers

                                  where c.CustomerID == "ALFKI"

                                  select c;

3.基于方法的查询语法

    var cust2 = edm.Customers.Where(c => c.CustomerID == "ALFKI");

4.排序分页

IQueryable<Customers> cust10 = (from c in customers

                                        orderby c.CustomerID

                                        select c).Skip(0).Take(10);

或者

var cust = edm.Customers.OrderBy(c => c.CustomerID).Skip(0).Take(10);

5.可使用的聚合运算符有Average、Count、Max、Min 和 Sum。

      var maxuprice = edm.Products.Max(p => p.UnitPrice);

      Console.WriteLine(maxuprice.Value);

6. 可以的连接有Join 和 GroupJoin 方法。GroupJoin组联接等效于左外部联接，它返回第一个（左侧）数据源的每个元素（即使其他数据源中没有关联元素）。

using (var edm = new NorthwindEntities())

    {

      var query = from d in edm.Order_Details

                  join order in edm.Orders

                  on d.OrderID equals order.OrderID

                  select new

                    {

                        OrderId = order.OrderID,

                        ProductId = d.ProductID,

                        UnitPrice = d.UnitPrice

                    };

        foreach (var q in query)

        Console.WriteLine("{0},{1},{2}",q.OrderId,q.ProductId,q.UnitPrice);

}

参考文章：

http://www.pin5i.com/showtopic-24045.html

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