EF linq: order of where and select in single() query

Question

Which query is optimized :

db.news.Select(c => new { c.Title, c.Date, c.ID })
       .SingleOrDefault(c => c.ID == 1);

or

db.news.Where(c => c.ID == 1)
       .Select(c => new { c.Title, c.Date })
       .SingleOrDefault();

I want this query:

select title, date  
where id = 1

in global which one is better where before select, or where after select?

I did not test this, but I am quite sure EF will build the same SQL query from both approaches. — SomeBody, Sep 21 '21 at 09:42
And you can observe the generated SQL to confirm: https://stackoverflow.com/questions/1412863/how-do-i-view-the-sql-generated-by-the-entity-framework — Johnathan Barclay, Sep 21 '21 at 09:44
@JohnathanBarclay may problem is both of them not get that query — foad abdollahi, Sep 21 '21 at 09:50

score 1 · Answer 1 · answered Sep 21 '21 at 09:52

1

Generally, Where before Select (Where first approach) is more performant, since it filters your result set first, and then executes Select for filtered values only.

answered Sep 21 '21 at 09:52

Kamal24h

70
2
9

EF builds a query based on all expressions prior to either a materializing operation (i.e. `ToList`, `AsEnumerable`, etc.) or encountering something that requires client-side evaluation and that feature is enabled. – Steve Py Sep 21 '21 at 10:19
1

Yet, I think Where first approach is performant. EF builds where first rapidly. However the performance difference between them, could be ignored for most of the applications. – Kamal24h Sep 21 '21 at 10:26

EF linq: order of where and select in single() query

1 Answers1