(adding to my answer from How to use array_agg in ecto to return structs)
If you want to fetch, say, 50 users along with all of their posts, you could write that:
users_query =
from(u in User, limit: 50) # etc
result =
users_query
|> Repo.all()
|> Repo.preload(:posts)
|> Map.new(fn u -> {u.id, u.posts} end)
What you don’t want to do is waste the database’s CPU encoding things into JSON to try to squeeze this into one query.
