LINQ - 数据表分组不同计数

Question

我正在尝试使用 linq 将 vb.Net 中的表连接在一起以返回主键的不同计数，但我似乎不太明白语法

这是创建表的代码

    Dim dtTable1 As New DataTable()
    dtTable1.Columns.Add("Table1Id", GetType(System.Int32))
    dtTable1.Columns.Add("MainEntityName", GetType(System.String))

    Dim dtTable2 As New DataTable()
    dtTable2.Columns.Add("Table2Id", GetType(System.Int32))
    dtTable2.Columns.Add("Table1Id", GetType(System.Int32))
    dtTable2.Columns.Add("SubEntityName", GetType(System.String))
    dtTable2.Columns.Add("JobType", GetType(System.Int32))
    dtTable2.Columns.Add("JobValue", GetType(System.Decimal))

    dtTable1.Rows.Add(1, 'Main Entity 1 Name')
    dtTable1.Rows.Add(2, 'Main Entity 2 Name')

    dtTable2.Rows.Add(1, 1, 'Sub Entity 1 Name', 1, 1000)
    dtTable2.Rows.Add(2, 1, 'Sub Entity 2 Name', 1, 2000)
    dtTable2.Rows.Add(3, 1, 'Sub Entity 3 Name', 1, 3000)
    dtTable2.Rows.Add(4, 2, 'Sub Entity 4 Name', 2, 4000)
    
    I would like join both tables together and do a distinct count of Table1Id and Table2Id
    
    In Sql I use this:
    SELECT COUNT(DISTINCT dbo.Table1.Table1Id) AS Table1IdCount, COUNT(DISTINCT dbo.Table2.Table2Id) AS Table2IdCount, 
    dbo.Table2.JobType, SUM(dbo.Table2.JobValue) AS Expr1
    FROM dbo.Table1 
        INNER JOIN dbo.Table2 ON dbo.Table1.Table1Id = dbo.Table2.Table1Id
    GROUP BY dbo.Table2.JobType
    
    This returns:
    1   3   1   6000
    1   1   2   4000        
    
    
    I would like to do this using LinQ
    
    Dim result = (From Table1 In dtTable1.AsEnumerable
                  Join Table2 In dtTable2.AsEnumerable
         On Table1.Field(Of Integer)("Table1Id") Equals Table2.Field(Of Integer)("Table1Id")
                  Group Table2 By ID = Table2.Field(Of Integer)("JobType") Into g = Group
                  Select New With {
                      Key ID,
                      .Table1IdCount = g.Distinct.Count(),
                      .Table2IdCount = g.Distinct.Count(),  ??????????
                      .JobValue = g.Sum(Function(r) r.Field(Of Decimal)("JobValue"))
                 })

有什么想法吗？

Answer 1

问题

.Table1IdCount = g.Distinct.Count(),

只会选择分组记录的计数，因此您需要更改此设置以仅从组中选择所需的字段，然后计算该字段的不同值，即类似于

.Table1IdCount = (From x In g Select x.Field(Of Integer)("Table1Id")).Distinct.Count() 

所以完整的查询可能类似于：

Dim result = (From Table1 In dtTable1.AsEnumerable
              Join Table2 In dtTable2.AsEnumerable
              On Table1.Field(Of Integer)("Table1Id") Equals Table2.Field(Of Integer)("Table1Id")
              Group Table2 By ID = Table2.Field(Of Integer)("JobType") Into g = Group
              Select New With 
              {
               .Table1IdCount = (From x In g Select x.Field(Of Integer)("Table1Id")).Distinct.Count() ,
               .Table2IdCount = (From x In g Select x.Field(Of Integer)("Table2Id")).Distinct.Count(),
               .JobType = ID,
               .JobValue = g.Sum(Function(r) r.Field(Of Decimal)("JobValue"))
              })
 
               

我更改了字段顺序以获得与您的 sql 查询类似的结果。