Yesod Esqueleto - How can I express selects with inner pagination? - sql

Question

I am doing a paginated resource, which will require an inner select, which I've already designed in sql terms. It has the following structure:
select *
from (
select w.*, d.distance
from `Work` w
inner join AdrDistance d on d.nhood2 = w.nhood
where d.nhood1 = 1 -- this will be a variable
order by d.distance
limit 0, 10 -- this will be pagination
) w
inner join WImage wi on wi.`work` = w.id
My entity definitions:
Work
...
WImage
work WorkId
url Text
AdrNhood
city AdrCityId
name Text maxlen=100
lat Double
lng Double
-- This is a view with a computed column I used for ordering
AdrDistance
nhood1 AdrNhoodId
nhood2 AdrNhoodId
distance Distance -- type Distance = Int - in Meters
How can I define such a select in Esqueleto, which would resemble such structure (by doing one single query of course)?
Update
I tried to follow this path:
worksByNhood nId offset' limit' =
from $ \wi -> do
(w, d) <- from $ \(w `InnerJoin` d) -> do
on $ d ^. AdrDistanceNhood2 ==. w ^. WorkNhood
where_ (d ^. AdrDistanceNhood1 ==. val nId)
orderBy [asc (d ^. AdrDistanceDistance)]
offset offset'
limit limit'
return (w, d)
where_ (wi ^. WImageWork ==. w ^. WorkId)
return (w, d ^. AdrDistanceDistance, wi)
But it didn't drive me to the correct solution. If someone can help me (even saying that I would be better doing several selects because what I am trying is not viable in Esqueleto), please, comment or answer my question.

Answer 1

I have read this issue on github
and I concluded Esqueleto wasn't designed to support selects in froms the way I was trying, so I did differently:
worksByNhood nId offset' limit' = do
works <- select $ from $ \(w `InnerJoin` d) -> do
on $ d ^. AdrDistanceNhood2 ==. w ^. WorkNhood
where_ (d ^. AdrDistanceNhood1 ==. val nId)
orderBy [asc (d ^. AdrDistanceDistance)]
offset offset'
limit limit'
return (w, d ^. AdrDistanceDistance)
works' <- forM works $ \(w#(Entity wId _), d) -> do
images <- select $ from $ \wi -> do
where_ (wi ^. WImageWork ==. val wId)
return wi
return (w, d, images);
return works'
It is not exactly what I was looking for, but for now I will use it. If somebody have a better approach, please, tell me.