Question

Before LINQ I would have my main application return the results of a SQL query into a dataSet. I would then transfer the dataset as a parameter to the external dll. Now I am bringing through a LINQ to SQL query that is returned as an IQueryable(Of vClientTable) object. I want to be able to transfer that set of vClientTable results to my external dll in order for the dll to work with the data included in the results.

I am probably doing it all wrong as well as trying to do it all wrong, but would like some advice on what would be the best method to use.

DB Query

Public Shared Function getClientData(ByVal clientID As Int32) As IQueryable(Of vClientTable)
Try
    Dim r = From p In dbLINQ.vClientTable _
       Where p.ltClientID = clientID _
       Order By p.cdCode _
       Select p
    Return r
Catch ex As Exception
    Return Nothing
End Try
End Function

App Sub that retrieves the Data through the DB Query

Dim recordData As IQueryable(Of vClientTable) = getClientData(clientID)

Call to External DLL sub

dataComplete = outputClientData(Now, recordData)

DLL sub

public static Boolean outputClientData(DateTime rptDate, IQueryable<vClientData> clientData)
    {
        //Do something with the data
        return true;
    }

Obviously in the external dll it has no idea what an IQueryable(vClientData) object is and even if I create a dbml file and datacontext in my external project for the dll that includes the same class to the DB table/view it still says that the objects are different types.

Any ideas how I should be proceeding with this?

Thanks

Answer 1

Can the external dll reference the assembly with the entities in them? Then you can return any collection/set/whatever of your types. That is the simplest use.

I would, however, tend to avoid exposing IQueryable<T> on the API, since it is very hard to guarantee full support for all operations, and hard to guarantee that the caller doesn’t break your DAL (accidentally or on purpose); I would have discreet operations that return known constructs such as List<T>, T[], etc.

If you can’t add a reference, then other options include:

• serialization (this is essentially how WCF transfers such objects; just enable serialziation on the designer surface, and use DataContractSerializer; you will need a matching data-contract at the other end, but it doesn’t have to be the same type)
• transfer into a known type such as DataTable – a bit like this and this, although I’m not really a fan of DataTable
• expose it as object, and use reflection (ho-hum)