如何使用Linq to SQL基于另一个表的前1个id进行联接？

Question

Right now, I receive the following error:

The ORDER BY clause is invalid in views, inline functions, derived tables, subqueries, and common table expressions, unless TOP or FOR XML is also specified.

This is my query:

var issues = from issue in this.IssueDatas
             join original in this.NoteDatas on issue.NoteDatas
                                                     .OrderBy(n => n.CreatedDate)
                                                     .Select(n => n.NoteId)
                                                     .First() equals original.NoteId
             join current in this.NoteDatas on issue.NoteDatas
                                                    .OrderByDescending(n => n.CreatedDate)
                                                    .Select(n => n.NoteId)
                                                    .First() equals current.NoteId
             select { whatever, i, want, to, select }

The SQL portion to grab those TOP 1 ids comes out like this:

SELECT whatever, i, want, to
FROM [dbo].[issue_Details] AS [t0]
INNER JOIN [dbo].[issue_notes] AS [t1] ON ((
    SELECT TOP (1) [t3].[id]
    FROM (
        SELECT [t2].[id], [t2].[issue_id]
        FROM [dbo].[issue_notes] AS [t2]
        ORDER BY [t2].[CreatedDate]
        ) AS [t3]
    WHERE [t3].[issue_id] = [t0].[IssueDetailsId]
    )) = [t1].[id]
INNER JOIN [dbo].[issue_notes] AS [t4] ON ((
    SELECT TOP (1) [t6].[id]
    FROM (
        SELECT [t5].[id], [t5].[issue_id]
        FROM [dbo].[issue_notes] AS [t5]
        ORDER BY [t5].[CreatedDate] DESC
        ) AS [t6]
    WHERE [t6].[issue_id] = [t0].[IssueDetailsId]
    )) = [t4].[id]

...but it should look more like this:

FROM [dbo].[issue_Details] AS [t0]
INNER JOIN [dbo].[issue_notes] AS [t1] ON (
    SELECT TOP (1) [t2].[id]
    FROM [dbo].[issue_notes] AS [t2]
    ORDER BY [t2].[CreatedDate]
    WHERE [t2].[issue_id] = [t0].[IssueDetailsId]
    ) = [t1].[id]
INNER JOIN [dbo].[issue_notes] AS [t4] ON (
    SELECT TOP (1) [t5].[id]
    FROM [dbo].[issue_notes] AS [t5]
    ORDER BY [t5].[CreatedDate] DESC
    WHERE [t5].[issue_id] = [t0].[IssueDetailsId]
    ) = [t4].[id]

I've tried using this.NoteDatas instead of issue.NoteDatas and manually applying the id filter, I've tried selecting the first note and then taking the id (reversing what I've typed above), I've tried using Take(int) instead of First() ... I just don't know what to do. The LINQ reads more straightforward than the SQL it generates.

Answer 1

By this:

 join original in this.NoteDatas on issue.NoteDatas
                                         .OrderBy(n => n.CreatedDate)
                                         .Select(n => n.NoteId)
                                         .First() equals original.NoteId

you are saying "order by CreatedDate, take first row from the results and check if it equals to NoteId". This is correctly gets rendered to this:

INNER JOIN [dbo].[issue_notes] AS [t1] ON ((
    SELECT TOP (1) [t3].[id]
    FROM (
        SELECT [t2].[id], [t2].[issue_id]
        FROM [dbo].[issue_notes] AS [t2]
        ORDER BY [t2].[CreatedDate]
        ) AS [t3]
    WHERE [t3].[issue_id] = [t0].[IssueDetailsId]
    )) = [t1].[id]

so t2.id is always same for any outer [t1].[id] but depends on only [t0].[IssueDetailsId]

Sample:

    var issues = new Tuple<int, string>[]
        {
            new Tuple<int, string>(1, "aaa"),
            new Tuple<int, string>(2, "bbb")
        };
    var notes = new Tuple<int, DateTime, string>[]
        {
            new Tuple<int, DateTime, string>(1, DateTime.Parse("01/01/2001"), "earliest for 1"),
            new Tuple<int, DateTime, string>(1, DateTime.Parse("02/01/2001"), "middle for 1"),
            new Tuple<int, DateTime, string>(1, DateTime.Parse("03/01/2001"), "latest for 1"),
            new Tuple<int, DateTime, string>(2, DateTime.Parse("10/01/2001"), "earliest for 2"),
            new Tuple<int, DateTime, string>(2, DateTime.Parse("11/01/2001"), "middle for 2"),
            new Tuple<int, DateTime, string>(2, DateTime.Parse("12/01/2001"), "once more middle for 2"),
            new Tuple<int, DateTime, string>(2, DateTime.Parse("13/01/2001"), "latest for 2")
        };

        var result =
            ctx.Set<Parent>().Select(i => new
                {
                    i.Id,
                    e = ctx.Set<Child>().Where(c => c.ParentId == i.Id).OrderBy(c => c.Name).FirstOrDefault(),
                    l = ctx.Set<Child>().Where(c => c.ParentId == i.Id).OrderByDescending(c => c.Name).FirstOrDefault()
                });

Answer 2

This is how I ended up changing the LINQ to have it work:

var issues = from issue in this.IssueDatas
             join original in this.NoteDatas on issue.NoteDatas
                                                     .Min(n => n.CreatedDate) equals original.CreatedDate
             join current in this.NoteDatas on issue.NoteDatas
                                                    .Max(n => n.CreatedDate) equals current.CreatedDate
             select { whatever, i, want, to, select }