Entity Framework Include performance

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Your second approach relies on the EF navigation property fixup process. The problem is though that every

query.Include(q => q.ItemNavN).Load();

statement will also include all the master record data along with the related entity data.

Using the same basic idea, one potential improvement could be to execute one Load per each navigation property, replacing the Include with either Select (for references) or SelectMany (for collections) – something similar to how EF Core processes the Includes internally.

Taking your second approach example, you could try the following and compare the performance:

var query = ctx.Filters.Where(x => x.SessionId == id)
    .Join(ctx.Items, i => i.ItemId, fs => fs.Id, (f, fs) => fs);

query.Select(x => x.ItemNav1).Load();
query.Select(x => x.ItemNav2).Load();
query.Select(x => x.ItemNav3).Load();
query.Select(x => x.ItemNav4).Load();
query.Select(x => x.ItemNav5).Load();
query.Select(x => x.ItemNav6).Load();

var result = query.ToList();
// here all the navigation properties should be populated

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