LINQ to SQL 模拟实现 ROW_NUMBER() OVER(ORDER BY ...) 的功能
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Ø 前言
本来是想使用 LINQ 实现类似 SQL: ROW_NUMBER() OVER(ORDER BY …) 的功能，但是貌似 LINQ 不支持，反正没找到解决办法，无奈使用了LINQ Select() 方法实现。
1) 需求，需要实现一下 SQL:
SELECT TOP 10 ROW_NUMBER() OVER(ORDER BY T.TotalMoney DESC) AS SN, * FROM
(
SELECT T2.Name, SUM(T2.Amount) AS TotalAmount, SUM(T2.TotalMoney) AS TotalMoney FROM Orders AS T1
LEFT JOIN OrderDetail AS T2 ON(T2.OrderId = T1.Id)
WHERE 1=1
AND T1.SalesUserId = 105
AND T1.PayStatusId = 2
AND (T1.OrderStatusId >=2 AND T1.OrderStatusId <= 8)
GROUP BY T2.Name
) AS T
2) 使用 LINQ Select() 方法
var result = (from t1 in DataContext.Orders
join t2 in DataContext.OrderDetail on t1.Id equals t2.OrderId into temp1
from t12 in temp1.DefaultIfEmpty()
where t1.SalesUserId == salesUserId && t1.PayStatusId == (int)OrderPayStates.Paid
&& (t1.OrderStatusId >= (int)OrderStates.Undelivered
&& t1.OrderStatusId <= (int)OrderStates.ReturnComplete)
group t12 by t12.Name into group1
select new
{
Name = group1.Key,
TotalAmount = group1.Sum(o => o.Amount),
TotalMoney = group1.Sum(o => o.TotalMoney)
}).OrderByDescending(o => o.TotalMoney).Take(10).AsEnumerable()
.Select((obj, index) => new
{
Name = obj.Name,
TotalAmount = obj.TotalMoney,
TotalMoney = obj.TotalMoney,
SN = index + 1
}).ToList();
l 注意：必须加上 AsEnumerable() 方法，且 AsEnumerable() 与 Select() 方法都为延迟查询方法。
3) 生成SQL:
exec sp_executesql N\'SELECT TOP (10)
[Project1].[C3] AS [C1],
[Project1].[Name] AS [Name],
[Project1].[C1] AS [C2],
[Project1].[C2] AS [C3]
FROM ( SELECT
[GroupBy1].[A1] AS [C1],
[GroupBy1].[A2] AS [C2],
1 AS [C3],
[GroupBy1].[K1] AS [Name]
FROM ( SELECT
[Extent2].[Name] AS [K1],
SUM([Extent2].[Amount]) AS [A1],
SUM([Extent2].[TotalMoney]) AS [A2]
FROM [dbo].[Orders] AS [Extent1]
LEFT OUTER JOIN [dbo].[OrderDetail] AS [Extent2] ON [Extent1].[Id] = [Extent2].[OrderId]
WHERE ([Extent1].[SalesUserId] = @p__linq__0) AND (2 = [Extent1].[PayStatusId]) AND ([Extent1].[OrderStatusId] >= 2) AND ([Extent1].[OrderStatusId] <= 8)
GROUP BY [Extent2].[Name]
) AS [GroupBy1]
) AS [Project1]
ORDER BY [Project1].[C2] DESC\',N\'@p__linq__0 bigint\',@p__linq__0=105
4) 最终结果（这是我想要的）
LINQ to SQL 实现 GROUP BY聚合ORDER BY
本地序列不能在查询运算符的 LINQ to SQL 实现中使用，但 Contains() 运算符除外