如何将两个具有相同列的From子句形成的集合合并到一起？

Question

想要在保存表前，对表中各行某一列不重复的值进行相关操作，集合类似如下语句。如何能将q1、q2合并到一起，并去除二者重复的值呢？即利用一个From语句形成一个集合（类似于SQL Server中的 UNION ALL功能）

   Dim q1 = From dr1 In table Where {DataRowState.Added, DataRowState.Modified}.Contains(dr1.RowState) Select dr1.某列 Distinct
   Dim q2 = From dr2 In table Where dr2.RowState = DataRowState.Deleted Select dr2("某列", DataRowVersion.Original) Distinct
      

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韩立学

Answer 1

請參考一下以下的link,

http://stackoverflow.com/questions/9633121/datatable-union

'建立空的DataTable
Dim dtResult = New DataTable("SC_1Funs")
dtResult.Columns.Add("c1", Type.GetType("System.String"))
dtResult.Columns.Add("c2", Type.GetType("System.String"))
'新增資料到DataTable之中
dtResult.Rows.Add(New String() {"c1-1", "c2-1"})
dtResult.Rows.Add(New String() {"c1-2", "c2-2"})

Dim dtResult2 = dtResult.Clone()
dtResult.Rows.Add(New String() {"c1-3", "c2-3"})
dtResult.Rows.Add(New String() {"c1-1", "c2-1"})

Dim comparer = New CustomComparer()

Dim dtUnion = dtResult.AsEnumerable.Union(dtResult2.AsEnumerable(), comparer).CopyToDataTable()

'other comparer class
Public Class CustomComparer
    Implements IEqualityComparer(Of DataRow)

    Public Function GetHashCode(ByVal obj As DataRow) As Integer Implements IEqualityComparer(Of DataRow).GetHashCode
        Return DirectCast(obj("c1"), String).GetHashCode()
    End Function

    Public Function Equals(ByVal x As DataRow, ByVal y As DataRow) As Boolean Implements IEqualityComparer(Of DataRow).Equals
        Return DirectCast(x("c1"), String).Equals(DirectCast(y("c1"), String))
    End Function

End Class

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亂馬客blog: http://www.dotblogs.com.tw/rainmaker/

Answer 2

Module Module1
    
    Sub Main()
        Dim dt As New DataTable
        Randomize()
        dt.Columns.Add("Id", GetType(Int32))
        For index = 1 To 10
            dt.Rows.Add(Rnd() * 5 + 1)
        Next
        dt.AcceptChanges()
 
        '打印
        For Each row In dt.Rows
            Console.WriteLine(row(0))
        Next
 
        '改变
        dt.Rows(0)(0) = 1
        dt.Rows(1)(0) = 2
        '删除
        dt.Rows(2).Delete()
        dt.Rows(3).Delete()
 
        Console.WriteLine("==========")
        Console.WriteLine("Changed：")
        '打印
        For Each row As DataRow In dt.Rows
            If (row.RowState = DataRowState.Modified) Then
                Console.WriteLine("From " & row(0, DataRowVersion.Original) & " To " & row(0, DataRowVersion.Current))
            End If
        Next
 
        Console.WriteLine("Deleted：")
        '打印
        For Each row As DataRow In dt.Rows
            If (row.RowState = DataRowState.Deleted) Then
                Console.WriteLine("Deleted Number：" & row(0, DataRowVersion.Original))
            End If
        Next
 
        '查询
        Dim result = ((From row In dt.AsEnumerable() Where row.RowState = DataRowState.Modified
                     Select row(0)).Union(From r In dt.AsEnumerable() Where r.RowState = DataRowState.Deleted Select r(0, DataRowVersion.Original))).Distinct()
 
        Console.WriteLine("======")
        '打印
        For Each row In result
            Console.WriteLine(row)
        Next
    End Sub
 
End Module

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