Question

我有一个包含此数据的数组（ID，Time和Name）：

var array = new[]
{
    new { ID = 1, Time = DateTime.ParseExact("12:01", "HH:mm", null), Name = "Peter" },
    new { ID = 2, Time = DateTime.ParseExact("12:06", "HH:mm", null), Name = "James" }, 
    new { ID = 3, Time = DateTime.ParseExact("12:03", "HH:mm", null), Name = "Jackie" },
    new { ID = 4, Time = DateTime.ParseExact("12:08", "HH:mm", null), Name = "Peter" }, 
    new { ID = 5, Time = DateTime.ParseExact("12:05", "HH:mm", null), Name = "James" },
    new { ID = 6, Time = DateTime.ParseExact("12:07", "HH:mm", null), Name = "Peter" },
};

数组上的以下语句产生正确的结果：

var result = array.OrderBy(x => x.Time).GroupBy(x => x.Name)
                  .SelectMany(x => x).ToArray();

结果：

Time: 2013/3/6 12:01:00, Name: Peter
Time: 2013/3/6 12:07:00, Name: Peter
Time: 2013/3/6 12:08:00, Name: Peter
Time: 2013/3/6 12:03:00, Name: Jackie
Time: 2013/3/6 12:05:00, Name: James
Time: 2013/3/6 12:06:00, Name: James

但是当我在EF和SQL Server中使用相同的语句时，顺序是错误的：

Time: 2013/3/6 12:03:00, Name: Jackie
Time: 2013/3/6 12:06:00, Name: James
Time: 2013/3/6 12:05:00, Name: James
Time: 2013/3/6 12:07:00, Name: Peter
Time: 2013/3/6 12:01:00, Name: Peter
Time: 2013/3/6 12:08:00, Name: Peter

这是SQL EF生成的：

SELECT 
[Extent2].[Id] AS [Id], 
[Extent2].[Time] AS [Time], 
[Extent2].[Name] AS [Name]
FROM   (SELECT DISTINCT 
    [Extent1].[Name] AS [Name]
    FROM [dbo].[testt1] AS [Extent1] ) AS [Distinct1]
INNER JOIN [dbo].[testt1] AS [Extent2]
ON ([Distinct1].[Name] = [Extent2].[Name]) OR 
   (([Distinct1].[Name] IS NULL) AND ([Extent2].[Name] IS NULL))

没有order by条款。

我忘记了什么？这是EF的错误吗？
如何从EF获得与数组相同的结果？

Answer 1

就像在SQL中一样：

第一组，然后订购：

var result = array.GroupBy(x => x.Name)
                  .Select(x => x.OrderBy(y => y.Time))
                  .SelectMany(x => x)
                  .ToArray();

但在你的情况下，我不明白为什么你会需要这个小组。每次看起来都不同，所以产生相同结果的简单版本（至少与您的测试数据一样）将是：

var result = array.OrderBy(x => x.Name)
                  .ThenBy(y => y.Time)
                  .ToArray();

查询的实体框架错误？

1 个答案: