VB。 NET：LINQ to SQL 相当于 Count - 按查询分组

Question

我正在尝试转换此查询（已经开始工作）：

Select building.Name, Count(people.ID) as NumberOfUser
From tblBuilding as building left outer join tblPeople as people on building.ID = people.buildingID
Group by building.Name

结果如下：

Name          | NumberOfUser
----------------------------
WestBuilding    50
EastBuilding    70
SouthBuilding   0
NorthBuilding   2

Linq 到 SQL。看看我的努力：

Dim db As New MyDatabaseDataContext
Dim query = From building In db.tblBuilding
            From people In db.tblPeople.Where(Function(x) building.ID = x.buildingID).DefaultIfEmpty
            Group building, people By building.ID, building.Name Into grp
                Select ID, Name, grp.Count
Return query.ToList

一开始似乎有效。但是当我检查一个没有人的建筑物时，Count列说有1。像这样：

Name          | NumberOfUser
----------------------------
WestBuilding    50
EastBuilding    70
SouthBuilding   1
NorthBuilding   2

因为那个楼虽然没有人，但是在结果查询中确实出现了一次，所以算了1次。换句话说，Count语句实际上是统计每个楼在结果中出现的次数table每栋楼里有多少人，因此没有人楼的结果是错误的。

有解决办法吗？

Answer 1

你是对的，要解决这个问题你需要测试是否有人，就像你在 count(people.Id)

中所做的那样

Dim db As New MyDatabaseDataContext
Dim query = From building In db.tblBuilding
            From people In db.tblPeople.Where(Function(x) building.ID = x.buildingID).DefaultIfEmpty
            Group building, people By building.ID, building.Name Into Group, Count(Not IsNothing(people))
'Select ID, Name, grp.Count
Return query.ToList

VB。 NET：LINQ to SQL 相当于 Count - 按查询分组

VB. NET: LINQ to SQL equivalent to Count - group by query

vb.net

linq-to-sql