LINQ 中的 where 子句子查询答案

【问题标题】：where clause subquery in LINQLINQ 中的 where 子句子查询
【发布时间】：2020-12-31 07:24:30
【问题描述】：

我正在尝试将我的 SQL 语法转换为 LINQ 查询，但我遇到了子查询问题。我想在表中选择带有 Id 的最大日期时间作为另一个选择命令的子查询，但我不知道下面的代码是对还是错。我在 Sql 中有什么

select ap.* ,aph.Lat as 'personLat',aph.Lng as 'personLng',l.cityId,l.Lat as 'LifecenterLat',l.lng as 'LifecenterLng',l.Id as 'LifeCenterId' 
from Applicant ap
inner join ApplicantAddressHistory aph on ap.Id = aph.ApplicantId 
inner join LifePlusCenter l on aph.CityId = l.CityId 
Where ap.FamilyRoleTypeId = '82e26080-fda6-4396-946c-40d0e267f1f3'  and aph.CreatedDate in (select max(CreatedDate) from ApplicantAddressHistory
where ApplicantAddressHistory.ApplicantId = ap.Id)
order by ap.NationalityCode

以及我在 linq 中尝试过的内容

        var innerJoinMultipleTables = from app in db.Applicant.Where(x => x.FamilyRoleTypeId == Guid.Parse("82e26080-fda6-4396-946c-40d0e267f1f3"))
                                          join aph in db.ApplicantAddressHistory on app.Id equals aph.ApplicantId         
                                          where aph.CreatedDate == db.ApplicantAddressHistory.Max(x => x.CreatedDate && x.Id=aph.Id)
                                          join l in db.LifePlusCenter on aph.CityId equals l.CityId
                                          let centerLat = l.Lat
                                          let centerLng = l.Lng
                                          orderby app.NationalityCode
                                          select new { app, aph.Lat, aph.Lng, l.CityId, l.Branch, centerLat, centerLng };

没有下面这行代码，我的 linq 可以正常工作。

  where aph.CreatedDate == db.ApplicantAddressHistory.Max(x => x.CreatedDate && x.Id=aph.Id)

我在 Linq 中需要像下面这样的代码作为子查询

select max(CreatedDate) from ApplicantAddressHistory where ApplicantAddressHistory.ApplicantId = '9836CEC4-EDCB-492C-9899-DF4279210CD2'

我终于试过了，它成功了，但不知道它的正确方法？！

           var innerJoinMultipleTables = from app in db.Applicant.Where(x => x.FamilyRoleTypeId == Guid.Parse("82e26080-fda6-4396-946c-40d0e267f1f3"))
                                          join aph in db.ApplicantAddressHistory on app.Id equals aph.ApplicantId
                                          let rept_max = (from c in db.ApplicantAddressHistory
                                                          where c.Id == app.Id
                                                          select c.CreatedDate).Max()

                                          where aph.CreatedDate == rept_max
                                          join l in db.LifePlusCenter on aph.CityId equals l.CityId


                                          let centerLat = l.Lat
                                          let centerLng = l.Lng
                                          orderby app.NationalityCode
                                          select new { app, aph.Lat, aph.Lng, l.CityId, l.Branch, centerLat, centerLng };

【问题讨论】：

我有一个关于 LINQ 查询的问题：子查询 where 语句是否使用正确的 ApplicantAddressHistory 列来获取最大日期？我认为这应该是正确的：where c.ApplicantId == app.Id

标签： sql linq linq-to-sql

【解决方案1】：

我不确定它在 Linq 中是如何工作的，但您可以修改您的查询，如下所示，以根据 CreatedDate 获取每个申请人 ID 的最新详细信息。

select ap.* ,aph.Lat as 'personLat',aph.Lng as 'personLng',l.cityId,l.Lat as 'LifecenterLat',l.lng as 'LifecenterLng',l.Id as 'LifeCenterId' 
from Applicant ap
inner join 
    (select *
    from
    (select *,row_number() over(partition by ApplicantId order by CreatedDate desc) rw
    from ApplicantAddressHistory
    ) p
    where p.rw=1
    ) aph 
    on ap.Id = aph.ApplicantId 
inner join LifePlusCenter l 
    on aph.CityId = l.CityId 
Where ap.FamilyRoleTypeId = '82e26080-fda6-4396-946c-40d0e267f1f3'  
/*
and aph.CreatedDate in (
select max(CreatedDate) from ApplicantAddressHistory
where ApplicantAddressHistory.ApplicantId = ap.Id
)
*/
order by ap.NationalityCode

【讨论】：

我在 SQL 中没有任何问题，但在 linq 中

【解决方案2】：

我终于想到了：

            var z = from app in db.Applicant
                    join aph in db.ApplicantAddressHistory on app.Id equals aph.ApplicantId
                    join l in db.LifePlusCenter on aph.CityId equals l.CityId

                    let createDate = app.ApplicantAddressHistory.Max(c => c.CreatedDate)

                    where createDate.HasValue && aph.CreatedDate == createDate

                    && app.FamilyRoleTypeId == Guid.Parse("82e26080-fda6-4396-946c-40d0e267f1f3")
                    let personLat = aph.Lat
                    let personLng = aph.Lng
                    let centerId = l.Id
                    let LifecenterLat = l.Lat
                    let LifecenterLng = l.Lng
                    orderby app.NationalityCode
                    select new { app, aph, l, app.Id, l.CityId, centerId, personLat, personLng, LifecenterLat, LifecenterLng };

【讨论】：