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In TPH inheritance, is there any difference between this: 

context.Firms.OfType<RedFirm>()

and this: 

context.Firms.Where(item => item is RedFirm);

In terms of performance?

abatishchev
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RobVious
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  • If there is any difference in performance at all it doesn't come from different SQL which is exactly the same for both queries: `SELECT ... FROM [Firms] WHERE [Discriminator] = 'RedFirm'`. – Slauma Dec 08 '13 at 00:18

1 Answers1

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OfType<T> returns an IEnumerable<T> (Or an IQueryable<T>, etc). It internally does an is and casts those objects to only return those of type T. OfType<TResult> also includes a short-circuit check that if the entire IEnumerable<T> is castable to IEnumerable<TResult> then it will perform significantly faster since it will not check each individual item in the collection.

Where does not change the returned type of IEnumerable<T>, and since you will have to cast them (if needed), OfType<T> should be slightly faster since it includes this call.

Related links: Why is OfType<> faster than Cast<>?

Community
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Michael Dunlap
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    This is all about Enumerable queries, not about Entity Framework. None of this applies. – usr Dec 07 '13 at 22:50
  • And EF doesn't matter in this case. No EF context has a translation for `is` or `OfType` as far as I understand. – Michael Dunlap Dec 08 '13 at 04:39
  • @MichaelDunlap, please edit your answer; I checked `System.Linq.Enumerable.OfType<>` and it doesn't have that short-circuit check you mentioned (.NET 4.7.1). – yv989c Feb 05 '19 at 20:33