[SOLVED] How to add an item to list in cycle in Elixir/Phoenix

How to add an item to list in cycle in Elixir/Phoenix

I'm studying Elixir/Phoenix and there is a task in front of me. I need to filter results from database in a cycle. Something like this:

user = Repo.get_by(User, api_token: token)
rooms = Repo.all(Room)
result = []
if !Enum.empty?(rooms) do
  Enum.each rooms, fn room ->
    users = Poison.decode!(room.users)
    if Enum.member?(users, user.id) do
       result = result ++ [room]
    end
  end
end
json(conn, %{"rooms" => result})

But this case don't allow me to append items to list, why? Because this is a functional language... Is there a way to append items to list in a cycle?

Oh yeah, maybe you ask me "Why you just don't get objects from the database by user id?" I'll say that the room.users store json array encoded in string

Solution

Whenever you want to select some items from a list, you can use Enum.filter/2. You can also use the in operator instead of Enum.member?/2.

user = Repo.get_by(User, api_token: token)
rooms = Repo.all(Room)
result = Enum.filter(rooms, fn room ->
  user.id in Poison.decode!(room.users)
end)

You can also use for instead of Enum.filter/2:

result = for room <- rooms, user.id in Poison.decode!(room.users), do: room