ryanditjia
How do I query a many-to-many relationship the Ecto way
Hello peeps, I feel this query isn’t concise (or isn’t Ecto-y) enough:
def list_posts_for(tag_id) do
query =
from(pt in PostTag,
where: pt.tag_id == ^tag_id,
left_join: p in Post,
on: p.id == pt.post_id,
select: p
)
Repo.all(query)
end
Posts and tags have many to many relationships + a join schema, and Ecto knows all about them.
Is it possible to start the query with from p in Post? Other ideas are welcome too.
First Post!
c4710n
Yes, you can.
Query post with id, and preload tags:
from p in Post,
join: t in assoc(p, :tags),
where: p.id == 1,
preload: [tags: p]
But, personally, I would like to use preload directly:
Repo.get(Post, 1) |> Repo.preload(:tags)
If you need tags associated with a post only, try
Ecto.assoc/2.
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