Question

I have problem and I’ve been looking for a week now on how to solve it. Yesterday I thought I solved but apparently I didn’t when I tried the query with new data added in my database.

Here’s my query

Public Function getTicketsByBeginstation(ByVal station As String) As Array

    Dim r As Array

    r = (From u In treinDataContext.Tickets Where u.ritId =
         (From v In treinDataContext.Rittens Where v.trajectId =
          (From s In treinDataContext.Trajectens Where s.beginstationId =
           ((From t In treinDataContext.Stations Where (t.naam = station) Select t.id).First) Select s.id).First Select v.id).First Select u.datumAankoop, u.betaalmethodeId, u.tijdAankoop, u.klasseId, u.ritId Order By datumAankoop Ascending).ToArray

    Return r

End Function

The problem I have is: when I have a station selected there are more than 1 trajecten (connections in English) but I had to use the .first else Visual Studio would give the error “the ‘=’ operator is not defined for ‘integers’ and ‘system.linq.IQueryable(of integer)”.

So I give the name of a station -> I have to select all trajectens with the given station as beginstation -> I have to select all ritten which have the given trajecten -> I have to select all tickets which have the given ritten

So: I have to show all tickets for a certain station.

Can anyone help me?

Answer 1

Could be that you’re looking for join instead

r = (From u In treinDataContext.Tickets 
       Join v In treinDataContext.Rittens 
       On u.ritId = v.id
       Join s In treinDataContext.Trajectens 
       On v.trajectId equals v.id
       JOIN t In treinDataContex 
       On s.beginstationId equals t.id 
       Where (t.naam = station)
       Select u.datumAankoop, 
               u.betaalmethodeId, 
               u.tijdAankoop,
               u.klasseId, 
               u.ritId 
       Order By  datumAankoop Ascending ).ToArray()

For more on joins see MSDN Article How to: Combine Data with LINQ by Using Joins (Visual Basic)