通过避免多个条目来计算客户的范围

Question

我有一个场景，角色和客户端存储在一个表中，我们必须在字典中获取它，并且必须确保对于一个用户，没有一个客户端有多个角色条目，并且如果它有最新的行版本记录。

在表格内，我们对用户、角色和客户端 ID 以及数据有唯一约束，如下所示：

#1- User,Role, Client Id, TimeStamp, rowVersion
    201,READ,101, 1/18/2019, 2
    201,WRITE,101, 1/18/2019, 1
    201,ADMIN,102, 1/18/2019, 3
    202,READ,102, 1/19/2019, 12

对于用户 201 - 客户端 101 只能有一个角色，以防有多个角色 - 排序后选择最新版本。 在上面的＃1中，它将计算到下面并存储在字典中 -

201,READ,101, 1/18/2019, 2
201,ADMIN,102, 1/18/2019, 3

如何在查询数据并存储在字典中时使用 LINQ 有效地实现这一点？

编辑 实际上 RowVersion 是 SQL Server 行版本，例如 0x0000000000019E12 只是为了简化我添加了数字来显示。

我们需要记住，对于给定的用户，我们正在为此 RoleScope 进行计算。在我的示例结果中，用户 201 的方法是

201,READ,101, 1/18/2019, 2
201,ADMIN,102, 1/18/2019, 3

以我想在 LINQ 中转换的 SQL 形式回答

select * from(
select UserId,ClientId,RowVersion,RoleCode,row_number() 
over(partition by ClientId order by RowVersion desc) as roworder
from dbo.UR where UserId=6
) temp
where roworder=1

Answer 1

如果我明白你想要什么。并假设 rowversion 只是一个 int（而不是 SqlServer timeStamp）

1. 使用GroupBy
2. OrderByrowVersion
3. 选择Last（最高）
4. ToDictionary

例子

var results = list.GroupBy(x => x.ClientId)
                  .Select(x => x.OrderBy(y => y.rowVersion).Last())
                  .ToDictionary(x => x.ClientId);

Answer 2

具有以下类：

class ClientRole
{
    public int ClientId { get; set; }
    public string Role { get; set; }
    public int RowVersion { get; set; }
}

试试这个：

var clientRoles = new List<ClientRole>
{
    new ClientRole { ClientId = 101, Role = "READ", RowVersion = 2 },
    new ClientRole { ClientId = 101, Role = "WRITE", RowVersion = 1 },
    new ClientRole { ClientId = 102, Role = "ADMIN", RowVersion = 2 },
    new ClientRole { ClientId = 102, Role = "OTHER", RowVersion = 12 }
};

var clientRolesDic = (
    from cr in clientRoles
    group cr by cr.ClientId into g
    select g.OrderByDescending(i => i.RowVersion).First()
    )
    .ToDictionary(k => k.ClientId);

Answer 3

似乎是一个简单的查询：

var clientRoles = new []
{
    new { ClientId = 101, Role = "READ", RowVersion = 2 },
    new { ClientId = 101, Role = "WRITE", RowVersion = 1 },
    new { ClientId = 102, Role = "ADMIN", RowVersion = 3 },
    new { ClientId = 102, Role = "READ", RowVersion = 2 },
};

var result =
    from cr in clientRoles
    orderby cr.ClientId, cr.RowVersion descending
    group cr by cr.ClientId into gs
    from g in gs.Take(1)
    select g;

这仅返回这些行：

    new { ClientId = 101, Role = "READ", RowVersion = 2 },
    new { ClientId = 102, Role = "ADMIN", RowVersion = 3 },

您的源数据中似乎有错误 - 最后一行应该有 2 的 RowVersion，而不是 12。

Answer 4

如果 Fiddle Stop 在这里工作是完整的工作解决方案，包括上面 Randall 建议的。

using System;
using System.Linq;
public class Simple {
  public static void Main() {
            var userRoles = (new[] 
            { 
            new { clientid=1 , rowVersion = 1 , role="READ" },
            new { clientid=1 , rowVersion = 2 , role="EDIT" },
            new { clientid=2 , rowVersion = 3 , role="ADMIN" },
            new { clientid=1 , rowVersion = 4 , role="VIEW" }
        });

var o = userRoles.OrderByDescending(x => x.rowVersion)
                .GroupBy(x => x.clientid)
                .SelectMany(g =>
                   g.Select((j, i) => new { j.rowVersion, j.role, rn = i + 1 })
                   );

    var z =  o.Select(x => new {x.rowVersion, x.role, x.rn}).Where(a => a.rn==1);

      var results = userRoles.GroupBy(x => x.clientid)
                  .Select(x => x.OrderByDescending(y => y.rowVersion).First());

          Console.WriteLine("Solution #1");

        foreach (var i in z)
        {
            Console.WriteLine("{0} {1} {2}", i.rowVersion, i.role, i.rn);
        }

      Console.WriteLine("Solution #2");

      foreach (var k in results)
        {
            Console.WriteLine("{0} {1}", k.rowVersion, k.role);
        }

  }
  }