saint
def get_all_post_by_user(user_id) do
query = from u in User,
where: u.id == ^user_id,
join: p in Post, on: p.user_id == u.id,
select: %{
user_id: u.id,
username: u.username,
title: p.title,
description: p.description
}
query |> Repo.all
end
i have this query but when i try to render it, it returns multiple set of data but same User with different Post.
like this.
[
%{user_id: 1,
username: "saint",
title: "test1",
description: "sample1"},
%{user_id: 1,
username: "saint",
title: "test2",
description: "sample2"}
]
Thanks in advance.
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idi527
You have a typo in the query. Should probably be
where: u.id == ^user_id.idi527
I think that’s how table joins work. In
psqlyou would get multiple rows. Maybe tryRepo.preloadorEcto.Query.preload.saint
Sorry for the typo and thanks for the quick response, ahm. i try to avoid using preload because of this https://medium.com/@alves.lcs/phoenix-ecto-preload-can-be-evil-96f877fb52f5. is it true? thanks
idi527
It might be. Depends on the amount of data that you query.
A join or
Ecto.Query.preloadmight be evil as well since then ecto would have to parse multiple almost identical rows like in your example and then put them all into some “parent” struct.Repo.preload, which fires a second query, might be more efficient in that case.saint
Okay thanks sir for the info
aphelion00
Can someone post an example of how to use preload to achieve this? I’m very new and haven’t wrapped my mind around it yet.
joaquinalcerro
There are different ways to use it. I think it’s best to check out the documentation:
Best regards
aphelion00
Already tried with the examples in documentation, all ended with Ecto.QueryErrors.
joaquinalcerro
Oh…
Can you share more details of what you are trying to do?
benwilson512
Welcome! We’re happy to help. In order for that to be possible though, it’s important that you provide full and complete information showing the code you tried, and the errors you got.