VB.NET LINQ to DataSet (SQL 'LEFT OUTER JOIN' alternative) - vb.net

Question

I would like to join two DataTables and create the third one from the result. The result DataTable should have three columns:
ID
Name
YearOfBirth
My Compile options:
Option explicit: On
Option strict: On
Option compare: Binary
Option infer: Off
Dim dr As DataRow
REM Dt1
Dim Dt1 As New DataTable
Dt1.Columns.Add("ID", GetType(Integer))
Dt1.Columns.Add("Name", GetType(String))
dr = Dt1.NewRow
dr("ID") = 1
dr("Name") = "Peter"
Dt1.Rows.Add(dr)
dr = Dt1.NewRow
dr("ID") = 2
dr("Name") = "Anna"
Dt1.Rows.Add(dr)
dr = Dt1.NewRow
dr("ID") = 3
dr("Name") = "John"
Dt1.Rows.Add(dr)
REM End Dt1
REM Dt2
Dim Dt2 As New DataTable
Dt2.Columns.Add("ID", GetType(Integer))
Dt2.Columns.Add("YearOfBirth", GetType(Integer))
dr = Dt2.NewRow
dr("ID") = 1
dr("YearOfBirth") = 1970
Dt2.Rows.Add(dr)
dr = Dt2.NewRow
dr("ID") = 2
dr("YearOfBirth") = 1980
Dt2.Rows.Add(dr)
REM End Dt2
Dim Dt3 As New DataTable
Dim query As IEnumerable(Of DataRow) = From dr1 In Dt1.AsEnumerable()
Group Join dr2 In Dt2.AsEnumerable()
On dr1.Field(Of Integer)("ID") Equals dr2.Field(Of Integer)("ID")
Into joined = Group
From j In joined.DefaultIfEmpty()
Select New With
{
.ID = dr1.Field(Of Integer)("ID"),
.Name = dr1.Field(Of String)("Name"),
.YearOfBirth = j.Field(Of Integer)("YearOfBirth")
}
Dt3 = query.CopyToDataTable
But I get the error message in editor (VS 2017):
"Error BC36754:
'IEnumerable(Of anonymous type: ID As Integer, Name As String, YearOfBirth As Integer)' cannot be converted to 'IEnumerable(Of DataRow)' because 'anonymous type: ID As Integer, Name As String, YearOfBirth As Integer' is not derived from 'DataRow', as required for the 'Out' generic parameter 'T' in 'Interface IEnumerable(Of Out T)'."

Answer 1

Select New without specifying class name as query result will return anonymous type (such like IEnumerable(Of AnonymousType)), and CopyToDataTable() throwing exception because IEnumerable(Of AnonymousType) cannot be converted directly to IEnumerable(Of DataRow).
Hence, you need to convert anonymous type into DataRow using additional Select method that iterates IEnumerable(Of AnonymousType) contents and returns DataRow with DataTable.NewRow() (using prepared DataTable which includes column names as result set):
' joined DataTable columns
Dim JoinedDT As New DataTable
JoinedDT.Columns.Add("ID", GetType(Integer))
JoinedDT.Columns.Add("Name", GetType(String))
JoinedDT.Columns.Add("YearOfBirth", GetType(Integer))
' other stuff
Dim query As IEnumerable(Of DataRow) = (From dr1 In Dt1.AsEnumerable() _
Group Join dr2 In Dt2.AsEnumerable() _
On dr1.Field(Of Integer)("ID") Equals dr2.Field(Of Integer)("ID") _
Into joined = Group _
From j In joined.DefaultIfEmpty() _
Select New With
{
.ID = dr1.Field(Of Integer)("ID"),
.Name = dr1.Field(Of String)("Name"),
.YearOfBirth = If(j IsNot Nothing, j.Field(Of Integer)("YearOfBirth"), 0)
}).Select(Function(r)
' use `DataTable.NewRow` here
Dim row As DataRow = JoinedDT.NewRow()
row("ID") = r.ID
row("Name") = r.Name
row("YearOfBirth") = r.YearOfBirth
Return row
End Function)
Dt3 = query.CopyToDataTable()
Reference:
Get linq to return IEnumerable<DataRow> result (C# version)