Question

I am using a code-first approach with Entity Framework, and a repository pattern to get entities back from my database. In my data model, each OverallEvent has many EventInConcept children. I want my GetEvents method to return an IList of OverallEvents, and I want the children of the aforementioned relationship to be concretized such that they can be accessed outside my DbContext (which AssessmentSystemContext is). This is the code I currently have:

public IList<OverallEvent> GetEvents() {
    using (var context = new AssessmentSystemContext()) {
        return context.OverallEvents
            .Select(evnt => new {
                OverallEvent = evnt,
                // evnt.EventsInConcept is a public virtual ICollection<EventInConcept>
                ConcreteEventsInConcept = evnt.EventsInConcept
            })
            .AsEnumerable()
            .Select(evntData => {
                evntData.OverallEvent.EventsInConcept = evntData.ConcreteEventsInConcept.ToList();
//              foreach (var eic in evntData.OverallEvent.EventsInConcept) {
//                  eic.Name = eic.Name;
//              }
                return evntData.OverallEvent;
            })
            .ToList();
    }
}

It gives me back a list of OverallEvent entities, which is fine, but the trouble is that if I try to access the child relationship EventsInConcept, I get an error. For example:

EventRepository repoEvent = new EventRepository();
var gotEvents = repoEvent.GetEvents();
var firstEventInConcept = gotEvents[0].EventsInConcept.FirstOrDefault();

… gives me the error “The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.”

I understood from the answer to an earlier question that if I projected EventsInConcept into a wrapper object, then explicitly set it in a later .Select call (ie. evntData.OverallEvent.EventsInConcept = evntData.ConcreteEventsInConcept.ToList();), it would concretize this one:many relationship and I would be able to access EventsInConcept outside of the DbContext, but it isn’t working here. Note that if I uncomment the foreach loop, it starts working, so to get it to work I have to explicitly set a property on every single entry of EventsInConcept. I don’t really want to have to do this (I’m picking an arbitrary property, .Name, which feels wrong anyway). Is there a better way?

Answer 1

Disable lazy loading for this query. It is of no use in that situation and when you dispose the context after the entities have been retrieved:

public IList<OverallEvent> GetEvents() {
    using (var context = new AssessmentSystemContext()) {
        context.Configuration.LazyLoadingEnabled = false;
        return ...
    }
}

It might be possible that EF doesn’t recognize that the collection has been loaded when you use a projection (instead of eager or explicit loading) and triggers lazy loading as soon as you access the collection.