zoukankan      html  css  js  c++  java
  • Linq实现t-Sql的各种连接

     在ORM框架大行其道的今天,对于.net行业的人,想要学好EF,那Linq的学习在势在必行啊。今天总结下平时比较常用的表连接的用法。

     Inner Join

         Linq: 

    1   var list = (from c in customerDb.Order
    2                             join o in customerDb.OrderItem on c.OrderId equals o.OrderItemId
    3                             select new { c = c.OrderId }).FirstOrDefault();

          生成的Sql

    1 SELECT TOP (1) 
    2 [Extent1].[OrderId] AS [OrderId]
    3 FROM  [dbo].[Orders] AS [Extent1]
    4 INNER JOIN [dbo].[OrderItems] AS [Extent2] ON [Extent1].[OrderId] = [Extent2].[OrderItemId]

    Left Join

          Linq:

    1      var list = (from c in customerDb.Order
    2                             join o in customerDb.OrderItem on c.OrderId equals o.OrderItemId
    3                             into Grp
    4                             from grp in Grp.DefaultIfEmpty()
    5                             select new { c = c.OrderId, grp = grp.OrderItemId }).FirstOrDefault();

          生成的Sql:

    1 SELECT TOP (1) 
    2 [Extent1].[OrderId] AS [OrderId], 
    3 [Extent2].[OrderItemId] AS [OrderItemId]
    4 FROM  [dbo].[Orders] AS [Extent1]
    5 LEFT OUTER JOIN [dbo].[OrderItems] AS [Extent2] ON [Extent1].[OrderId] = [Extent2].[OrderItemId]

     Cross Join

            Linq:   

    1     var list = (from c in customerDb.Order
    2                             from o in customerDb.OrderItem 
    3                             select new { c = c.OrderId,o=o.OrderItemId }).FirstOrDefault();

            生成的Sql:

    1 SELECT TOP (1) 
    2 [Extent1].[OrderId] AS [OrderId], 
    3 [Extent2].[OrderItemId] AS [OrderItemId]
    4 FROM  [dbo].[Orders] AS [Extent1]
    5 CROSS JOIN [dbo].[OrderItems] AS [Extent2]

      总结:右连接其实就是换下两个表的顺序位置,

              全连接就是把左外连接的结果拼接起来去重就行。

              用顺ef后,可以加速开发效率,期待那一天早日到来,加油啊!!!

  • 相关阅读:
    图论分支-Tarjan初步-边双联通分量
    图论分支-Tarjan初步-割点和割边
    简谈图论重要性&&图论总结
    Angular本地数据存储LocalStorage
    (转)AngularJS中使用的表单验证
    (转)AngularJS判断checkbox/复选框是否选中并实时显示
    (转载)JavaScript世界万物诞生记
    (转载)关于My97 datepicker与Angular ng-model绑定问题解决。
    mysql
    mysql
  • 原文地址:https://www.cnblogs.com/JaggerMan/p/4538008.html
Copyright © 2011-2022 走看看