VB.Net LINQ - left outer join between two datatables - limit to one row

Question

I have an issue with LINQ in vb.net. Basically I want create LEFT JOIN between two datatables.

This is the info of the two datatables:

Dim vDT1 As Ne         


        

Answer 1

The key is to call FirstOrDefault() on the group. Then you either have the first row in the group or Nothing.

Dim query =
    From a In vDT1.AsEnumerable
    Group Join b In vDT2.AsEnumerable
        On a.Field(Of String)("Key") Equals b.Field(Of String)("Key")
        Into Group
    Let b = Group.FirstOrDefault
    Select Key = a.Field(Of String)("Key"),
           Data1 = a.Field(Of String)("Data1"),
           Data2 = a.Field(Of String)("Data2"),
           Data3 = If(b Is Nothing, Nothing, b.Field(Of String)("Data3")),
           Data4 = If(b Is Nothing, Nothing, b.Field(Of String)("Data4"))

    ' Or Simply
    'Select a, b