zoukankan      html  css  js  c++  java
  • Linq排序方式与Lambda排序方式比较以及OrderBy、ThenBy的使用

    Linq排序方式与Lambda排序方式比较以及OrderBy、ThenBy的使用

    沿用之前某一篇文章的实体类与EF操作类代码。数据库中增加几条数据

    Linq 的排序方式,下面例子是根据RoleId 升序,Name降序

    EFContext<Member> efMemberContext = new EFContext<Member>();
    var memberSet = efMemberContext.Set<Member>().Include("Role");
    var memberList = from m in memberSet
                     orderby m.RoleId ascending, m.Name descending
                     select m;
    
    foreach (Member item in memberList)
    {
        Console.WriteLine("{0},Role:{1}",item.Name,item.Role.Name);
    }

    输出结果如下:

    SQL Profiler如下:

     同样的方式如果用Lambda排序,先猜想如下,

    复制代码

    EFContext<Member> efMemberContext = new EFContext<Member>();
    var memberSet = efMemberContext.Set<Member>().Include("Role");
    var memberList = memberSet.OrderBy(m => m.RoleId).OrderByDescending(m => m.Name);
    foreach (Member item in memberList)
    {
        Console.WriteLine("{0},Role:{1}",item.Name,item.Role.Name);
    }

    复制代码

    运行程序发现与linq方式的不一致,

    SQL Profile如下:

    发现连续调用OrderBy或者OrderByDescending之后,以最后一个为准排序,这时ThenBy就派上了用场。

    ThenBy是使用OrderBy或者OrderByDescending之后,再次对结果进行二次排序

    复制代码

    EFContext<Member> efMemberContext = new EFContext<Member>();
    var memberSet = efMemberContext.Set<Member>().Include("Role");
    var memberList = memberSet.OrderBy(m => m.RoleId).ThenByDescending(m => m.Name);
    foreach (Member item in memberList)
    {
        Console.WriteLine("{0},Role:{1}",item.Name,item.Role.Name);
    }

    复制代码

    如果想数据库中多个列排序一致,可以先OrderBy(或者OrderByDescending)后ThenBy(或者ThenByDescending),也可以在OrderBy或者OrderByDescending直接指定多个属性,这样生成的SQL就是多个列的排序(排序一致asc/desc)

    复制代码

    EFContext<Member> efMemberContext = new EFContext<Member>();
    var memberSet = efMemberContext.Set<Member>().Include("Role");
    var memberList = memberSet.OrderBy(m => new { m.RoleId, m.Name });
    foreach (Member item in memberList)
    {
        Console.WriteLine("{0},Role:{1}",item.Name,item.Role.Name);
    }

    复制代码

     

  • 相关阅读:
    108. Convert Sorted Array to Binary Search Tree
    107. Binary Tree Level Order Traversal II
    106. Construct Binary Tree from Inorder and Postorder Traversal
    105. Construct Binary Tree from Preorder and Inorder Traversal
    104. Maximum Depth of Binary Tree
    103. Binary Tree Zigzag Level Order Traversal
    102. Binary Tree Level Order Traversal
    系统和进程相关信息
    文件I/0缓冲
    系统编程概念(文件系统mount等函数的使用)
  • 原文地址:https://www.cnblogs.com/grj001/p/12224747.html
Copyright © 2011-2022 走看看