[英]Entity Framework subquery in join
I have a problem using a subquery inside my join operator. 我在连接运算符中使用子查询时遇到问题。
I'd like to know how I can make my LINQ query better. 我想知道如何更好地使我的LINQ查询。
I want to become a query like this: 我想成为这样的查询:
SELECT Submissions.Title, SubmissionStatusEvents.ToStatus, SubmissionStatusEvents.ToStatusId, SubmissionStatusEvents.Created, SubmissionComments.Created, Content =
CASE
WHEN SubmissionComments.Type = '1'
THEN SubmissionComments.Content
ELSE NULL
END, AspNetUsers.UserName, AspNetUsers.AvatarId , Projects.Name, Comapnies.LogoId
FROM Submissions
JOIN SubmissionComments ON SubmissionComments.Id =
(
select TOP 1 Id
From SubmissionComments
where SubmissionComments.SubmissionId = Submissions.Id
Order by SubmissionComments.Created desc
)
JOIN SubmissionStatusEvents ON SubmissionStatusEvents.Id =
(
select TOP 1 Id
From SubmissionStatusEvents
where SubmissionStatusEvents.SubmissionId = Submissions.Id
Order by SubmissionStatusEvents.Created desc
)
JOIN AspNetUsers ON SubmissionComments.CommenterId=AspNetUsers.Id
JOIN Projects ON Projects.Id = Submissions.ProjectId
JOIN Companies ON Projects.CompanyId = Companies.ID
I tried it with following LINQ: 我尝试了以下LINQ:
(from submission in _ctx.Submissions
join status in _ctx.SubmissionStatusEvents on (from s in _ctx.SubmissionStatusEvents where s.IsPublic && s.SubmissionId == submission.Id orderby s.Created descending select s.Id).First() equals status.Id
join comment in _ctx.SubmissionComments on (from c in _ctx.SubmissionComments where c.IsPublic && c.SubmissionId == submission.Id orderby c.Created descending select c.Id).First() equals comment.Id
join user in _ctx.Users on comment.CommenterId equals user.Id
join project in _ctx.Projects on submission.ProjectId equals project.Id
join company in _ctx.Companies on project.CompanyId equals company.Id
where submission.SubmitterId == userId
where status.IsPublic
select new SubmissionWithLastEventChangeDto
{
Id = submission.Id,
Title = submission.Ttile,
Status = status.ToStatus,
StatusId = status.ToStatusId,
StatusChange = status.Created,
ProjectId = project.Id,
ProjectName = project.Name,
ProjectType = project.Type,
MaxPayout = project.ExceptionalPayout ?? project.CriticalPayout,
LogoId = company.LogoId,
LastComment = new LastEventChangeDto
{
UserName = user.UserName,
AvatarId = user.AvatarId,
Created = comment.Created,
Type = comment.Type,
Content = comment.Type == EntityEnum.SubmissionCommentType.Event ? comment.Content : null
}
}).ToListAsync();
However this LINQ query causes multiple queries: 但是,此LINQ查询会导致多个查询:
I tried many things. 我尝试了很多东西。 Like using let as in this example Stack Overflow answer .
就像在这个例子中使用let一样Stack Overflow回答 。 My final attempt is based on this Stackoverflow answer
我的最后一次尝试是基于Stackoverflow的回答
I also tried to use .Take(1) instead of .First() 我也尝试使用.Take(1)代替.First()
If someone could point me in the correct direction I would be happy. 如果有人能指出我正确的方向,我会很高兴。 Sincerely, Brecht
真诚的,布莱希特
I would suggest utilizing the LINQ GroupJoin
(similar to LINQ LEFT OUTER JOIN
emulation, but instead of DefaultIfEmpty
use OrderByDescending
+ Take
): 我建议使用LINQ
GroupJoin
(类似于LINQ LEFT OUTER JOIN
仿真,但不使用DefaultIfEmpty
使用OrderByDescending
+ Take
):
(from submission in db.Submissions
join status in _ctx.SubmissionStatusEvents on submission.Id equals status.SubmissionId into statusGroup
from status in statusGroup.OrderByDescending(status => status.Created).Take(1)
join comment in _ctx.SubmissionComments on submission.Id equals comment.SubmissionId into commentGroup
from comment in commentGroup.OrderByDescending(comment => comment.Created).Take(1)
... the rest (no change)
Of course the generated SQL query will be different (the construct translates to CROSS APPLY
) but the result should be the same. 当然生成的SQL查询将是不同的(构造转换为
CROSS APPLY
)但结果应该是相同的。
Your query feels a little odd (may be to do with the structure), but I would be tempted to try something like this: 您的查询感觉有点奇怪(可能与结构有关),但我很想尝试这样的事情:
(from submission in _ctx.Submissions
where submission.SubmitterId == userId
select new SubmissionWithLastEventChangeDto
{
Id = submission.Id,
Title = submission.Ttile,
Status = submission.SubmissionStatusEvents.OrderByDescending(e => e.Created).First().ToStatus,
StatusId = submission.SubmissionStatusEvents.OrderByDescending(e => e.Created).First().ToStatusId,
StatusChange = submission.SubmissionStatusEvents.OrderByDescending(e => e.Created).First().Status,,
ProjectId = submission.Project.ProjectId,
ProjectName = submission.Project.Name,
ProjectType = submission.Project.Type,
MaxPayout = submission.Project.ExceptionalPayout ?? submission.Project.CriticalPayout,
LogoId = submission.Project.Company.LogoId,
LastComment = new LastEventChangeDto(submission.SubmissionComments.OrderByDescending(e => e.Created).First())
}).ToListAsync();
//CTOR for this class
public LastEventChangeDto(SubmissionComment comment)
{
UserName = comment.User.UserName,
AvatarId = comment.User.AvatarId,
Created = comment.Created,
Type = comment.Type,
Content = comment.Type == EntityEnum.SubmissionCommentType.Event ? comment.Content : null
}
Might be a bit easier to follow than all the many joins in linq. 可能比linq中的所有连接更容易遵循。
I might also suggest a Dto to pass through your flatted status fields as well - could take a SubmissionStatus as a parameter. 我也可能建议Dto也可以通过你的平面状态字段 - 可以将SubmissionStatus作为参数。
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