Question

I am having an issue that I believe can be resolved with a simple understanding. I am using Entity Framework 5 with code first and POCO. I have all navigational properties properly configured (virtual) for all of my POCO objects. The problem occurs when I query for an object (POCO) and then return that POCO as a result. All navigational properties for the POCO are null’ed:

class PocoParent  { // all of these are properties (get/set)
    public int Id;
    public string ParentProperty;
    public virtual PocoChild NavProperty;
}
class PocoChild {
    public int Id;
    public int ParentId;
    public string Name;
    public virtual PocoParent Parent;
}

Inside a repository class that handles my queries:

IEnumerable<PocoChildren> GetAllChildrenFor(int parentId) {
    using(Context db = new Context()) {
        var pcs = db.PocoParents.Where(p => p.Id == parentId);
        return pcs;
    }
}

Now use the repository:

...
var children = repo.GetAllChildrenFor(queriedParent.Id);
...

Now use the results from the repository and this is where the error occurs:

...
foreach(child in children) {
   if(child.Parent.NavProperty == "null") {  !!! Exception: child.Parent ObjectContext already disposed
   }
}
...

How can I dispose the ObjectContext (to detach the POCO object), but retain at least one level of navigational properties? I have looked endlessly for a solution, but I am stumped as the solutions are all conflicting one another on how to do it.

— Recap —-
With the answer given below, if I were to change the query in the repository to the following:

IEnumerable<PocoChildren> GetAllChildrenFor(int parentId) {
    using(Context db = new Context()) {

        var pcs = db.PocoParents.Include(p => p.Select(prop => prop.Parent).Where(p => p.Id == parentId);

        return pcs;
    }
}

Would that return the all the enities and they will contain a non-null .Parent property, or whatever property I specify?

Answer 1

Lazy loading is enabled by default and that is why the navigable properties are null. Lazy loading means the navigable properties aren’t loaded until they are requested. And if the context is gone when they are requested, they get set to null since they can’t be loaded.

To get around this, you need to disable lazy loading or explicitly (and eagerly) load the properties you need.

This MSDN magazine article is a good source to help you decide which route is best for you.