Materializing an ICollection structure containing subclasses

Question

I\'m reviewing some code that was written in the EF 4 days because it stands out during performance benchmarking.

The purpose of the code is to materialize an ICol

Answer 1

It cannot be said in advance if the performance will be better (sometimes executing a single complex query, especially with sub collection includes may have actually negative impact), but you can minimize the number of database queries to K, where K is the number of subclass types that need additional includes.

You need to base the LoadSubclasses method on IQueryable representing all base entities, and execute one query per each subclass type using OfType filter:

private void LoadSubclasses(IQueryable baseQuery)
{
    // SubA
    baseQuery.OfType()
        .Include(x => x.Ref1.Options)
        .Load();
   // Similar for other subclasses
}

The usage with your sample would be:

var parent = ctx.Parents.Include(p => p.Base).Where(...).Single();
LoadSubclasses(ctx.Entry(parent).Collection(p => p.Base).Query());

or more generally:

var parentQuery = ctx.Parents.Where(...);
var parents = parentQuery.Include(p => p.Base).ToList();
LoadSubclasses(parentQuery.SelectMany(p => p.Base));