How can I load multiple levels when lazy loading in EF Core?

Question

I have a program using C# / WPF and SQL Server with EF Core 5. Sometimes I use eager loading, for example:

(from r in MyContext.Refractions where r.Id == id select r)
    .Include(r => r.RightLens)
    .ThenInclude(l => l.Prisms);

and so on. This is a database of optical data, hence the field names. Refractions are linked to (eye) Examinations.

When I want to lazy load, I use the following:

MyContext.Entry(patient)
         .Collection(e => e.Examinations).Load();

My question is, when using the second, lazy option, is there a way to also load associated data (the equivalent of .Include for the Load method)?

So for example, I want the equivalent of:

MyContext.Entry(patient)
         .Collection(e => e.Examinations)
         .Load().Include(r => r.Refractions);

or do I need to detect that the Refractions collection is not loaded somewhere in my view model and then load it manually when required?

It is not lazy load. It is explicit load. You have to configure context for Lazy load and make collection properties virtual learn.microsoft.com/en-us/ef/core/querying/related-data/… — Svyatoslav Danyliv
– Svyatoslav Danyliv, Commented Apr 22, 2021 at 16:41

Dejan · Accepted Answer · 2024-02-14 14:00:30Z

1

As I don't think this is possible yet, you could write some methods like those:

public IEagerLoadedQueryable<E, P> LoadRelated<E, P>(IQueryable<E> query, Expression<Func<E, P>> navProperty) where E : class {
  var q= query.Include(navProperty);
  return new EagerLoadedQueryable<E, P>(q);
}

public IEagerLoadedQueryable<E, Prop> ThenLoadRelated<E, Prev, Prop>(IEagerLoadedQueryable<E, IEnumerable<Prev>> query, Expression<Func<Prev, Prop>> navProperty) where E : class {
  var q= (IIncludableQueryable<E, IEnumerable<Prev>>)query;
  return new EagerLoadedQueryable<E, Prop>(q.ThenInclude(navProperty));
}


public IEagerLoadedQueryable<E, Prop> ThenLoadRelated<E, Prev, Prop>(IEagerLoadedQueryable<E, Prev> query, Expression<Func<Prev, Prop>> navProperty) where E : class {
  var q= (IIncludableQueryable<E, Prev>)query;
  return new EagerLoadedQueryable<E, Prop>(q.ThenInclude(navProperty));
}

edited Feb 14, 2024 at 14:00

Dejan

10.6k8 gold badges84 silver badges129 bronze badges

answered Apr 22, 2021 at 14:23

Mr.Deer

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