Question

This scenario comes up often, now that I use LinkToSql and the classes it creates.

Classic scenario – two tables:

Member
ID
Name
…

Membership
ID
MemberID (foreign key)
Start (datetime)
Expiration (datetime)
…

An active membership would be one where now is between start and expiration.

To find out if a user has an active membership, I have created this partial class to extend on the LinkToSql-generated Member-class:

Partial Public Class Member
    Public ReadOnly Property HasActiveMembership() As Boolean
        Get
            Dim activeMembershipCount As Integer = (From m In Me.Memberships _
                                Where m.MemberId = Me.MemberId _
                                And m.StartDate < Now And m.ExpirationDate > Now() _
                                Select m).Count

            If activeMembershipCount > 0 Then Return True Else Return False

        End Get
    End Property
End Class

This works great for one member, but when I want to list 700 members and if they have active membership or not, it makes 700+ calls to the database.

How should I change my model/classes?

I could create a query just for lists, where make the entire thing into one query, which is pretty straightforward, but I would like to avoid that, if I could.

Answer 1

You have a few options; for example, you could use DataLoadOptions.LoadWith or DataLoadOptions.AssociateWith to fetch the data eagerly – however, the optimal approach depends on how you are using it.

For example, you could write a “users with active membership” query (either in LINQ using Any, or with a SPROC/UDF). That would then be 1 round trip, but is arguably less object-centric (and more query centric). Which might be fine…