You may just return countRows as Gaël said. However, there's a catch:
GHC won't have enough information to typecheck the code and infer
which table you're talking about. You'll probably need something such
as:
count <-
select $
from \(foo :: SqlExpr (Entity Foo)) ->
return countRows
Alternatively, you could constraint the type via an unused expression:
count <-
select $
from \foo ->
let _ = foo ^. FooId -- constraint the type of foo
return countRows
Both code snippets are untested. Have fun =).
Cheers,
On Fri, Nov 23, 2012 at 9:16 AM, Gaël Deest
Le 23/11/12 12:04, Erik de Castro Lopo a écrit :
Francesco Mazzoli wrote:
Have you looked at
http://hackage.haskell.org/packages/archive/esqueleto/0.2.8/doc/html/Databas...? I didn’t try, but it looks promising.
The examples in that section still suggest that the SELECT statement that is run against the database returns an element for each row whereas the what I'm hoping for is a single element returned, the row count.
Erik
Never played with Esqueleto, but it looks to me like the following would work:
count <- select $ from \foo -> do return countRows
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-- Felipe.