Question

i have 2 datatables tables which have the same columns but with different data and some times there are rows the share the same ID

i want to join those to table where ID of some row in table2 doesn’t exist in table1

so if i the following tables
ID Name
1  A
2  B
3  C

ID Name
5  D
1  A
2  B
3  C

the from joining would be

ID Name
1  A
2  B
3  C
5  D

here is what i tried

 Dim q = From e In tbl1.AsEnumerable Join r In tbl2.AsEnumerable On e.Field(Of Integer)("id") Equals r.Field(Of Integer)("id")

but no idea on how do i get this to a datatable

Answer 1

LINQ is not all that good in working with DataTable but you could do something like this:

Dim diff = tbl2.AsEnumerable().Except(tbl1.AsEnumerable(), New DataRowComparer())

Dim tbl = tbl1.Copy()
For Each dataRow As DataRow In diff
    tbl.ImportRow(dataRow)
Next

You need to create an IEqualityComparer to define how to compare DataRows. I decided to compare only their Id value but you could compare every column in a similar manner:

Public Class DataRowComparer
    Implements IEqualityComparer(Of DataRow)

    Public Function Equals(ByVal x As DataRow, ByVal y As DataRow) As Boolean Implements IEqualityComparer(Of DataRow).Equals
        Return CInt(x("Id")) = CInt(y("Id"))
    End Function

    Public Function GetHashCode(ByVal obj As DataRow) As Integer Implements IEqualityComparer(Of DataRow).GetHashCode
        Return CInt(obj("Id")).GetHashCode()
    End Function
End Class