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Should you use Include or a projection (Select) in EF Core?

Entity Framework & EF Core Querying Intermediate 2–3 Yrs3–5 Yrs Architecture 1 min read

Quick Answer

Include loads full related entities and tracks them — right when you need to modify the graph. A projection (Select into a DTO) pulls only the columns you list, across joins, with no tracking — right for read-only screens and API responses, and usually faster.

It depends on whether I'm going to change the data. If I need to load an order, modify its lines and save, I use Include so I get the real tracked entities. If it's a read — a list screen, an API response — I project into a DTO with Select, because EF then only fetches the exact columns I named, joins as needed, and doesn't track anything, which is faster and lighter. And if I ever Include several collections at once I turn on AsSplitQuery to avoid the row explosion from the cartesian join.

  • Include(o => o.Lines).ThenInclude(l => l.Product) — you get whole Order, Line, Product entities; use for edit scenarios.
  • Select(o => new OrderDto { o.Id, LineCount = o.Lines.Count, Total = o.Lines.Sum(l => l.Price) }) — one query, minimal columns, no change tracker.
  • Multiple collection Includes cause a cartesian explosion — add AsSplitQuery().
  • Rule: reading → project; writing → include.
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