Can we use Phoenix LiveView Stream more than one time in the View

Phoenix Forum Questions / Help
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1

I’ve just trying out LiveView for the first time, and I’ve generated a live endpoint with mix phx.gen.live TodoService Todo todos ..., I have pulled in the generated routes to my routes file and it’s working.

Just to test things out, I tried rendering some HTML by editing the generated Heex, and it’s not working.

...
...
<ul
  id="todos_list"
  phx-update={match?(%Phoenix.LiveView.LiveStream{}, @rows) && "stream"}
>
  <li
    :for={{dom_id, todo} <- @streams.todos}
    id={dom_id}
  >
    <span><%= todo.name %></span>
  </li>
</ul>

<.table
  id="todos"
  rows={@streams.todos}
  row_click={fn {_id, todo} -> JS.navigate(~p"/todos/#{todo}") end}
>
  <:col :let={{_id, todo}} label="Name"><%= todo.name %></:col>
  <:col :let={{_id, todo}} label="Notes"><%= todo.notes %></:col>
...
...

I’m getting the below error:

KeyError at GET /todos

`key :rows not found in: %{
  socket: #Phoenix.LiveView.Socket<
    id: "phx-F70FhIK4AoARkQvC",
    endpoint: TodoAppWeb.Endpoint,
    view: TodoAppWeb.TodoLive.Index,
    parent_pid: nil,
    root_pid: nil,
    router: TodoAppWeb.Router,
    assigns: #Phoenix.LiveView.Socket.AssignsNotInSocket<>,
    transport_pid: nil,
    ...
  >,
  __changed__: %{page_title: true, streams: true, todo: true},
  flash: %{},
  page_title: "Listing Todos",
  live_action: :index,
  streams: %{
    __changed__: MapSet.new([:todos]),
    todos: %Phoenix.LiveView.LiveStream{
      name: :todos,
      dom_id: #Function<3.112696910/1 in Phoenix.LiveView.LiveStream.new/4>,
      ref: "0",
      inserts: [
        {"todos-3", -1,
         %TodoApp.TodoService.Todo{
           __meta__: #Ecto.Schema.Metadata<:loaded, "todos">,
           id: 3,
           name: "one",
           notes: "one none",
           is_completed: false,
           is_archived: false,
           inserted_at: ~U[2024-03-15 18:53:37Z],
           updated_at: ~U[2024-03-15 18:53:37Z]
         }, nil}
      ],
      deletes: [],
      reset?: false,
      consumable?: false
    },
    __configured__: %{},
    __ref__: 1
  },
  todo: nil
}`

Guess I can’t subscribe or use a stream more than twice in a View??

Can someone elaborate on how it works. The docs is silent on streams.

2

Hello and welcome to Elixir Forum!

The error is saying there is no :rows assign. This is most likely your problem:

phx-update={match?(%Phoenix.LiveView.LiveStream{}, @rows) && "stream"}

You probably mean @streams.todos instead of @rows.

2 Likes
3

Yes, I found it and rectified it.

Btw, can you point me to any docs or posts about LiveStream?

4

I’m guessing you copied that line from the the table component?

The only documentation I’m aware of for streams is for the functions themselves. %Phoenix.LiveView.LiveStream{} is simply the struct that holds data about each stream and AFAIK is considered opaque, ie, you aren’t supposed to manipulate it directly. It is what you get when you say @streams.my_stream, though.

This line from the table component:

phx-update={match?(%Phoenix.LiveView.LiveStream{}, @rows) && "stream"}

is just doing some type checking to see if you passed a stream or not. This is so it can support both streams and a simple list. It’s making use of the fact that passing nil or false to a component attribute will cause the attribute itself not to render at all, so if match?(%Phoenix.LiveView.LiveStream{}, @rows) returns false, it’ll get phx-update={false} otherwise if it’s a stream it will get phx-update="stream".

Sorry if I’m not explaining this very well.

1 Like
5

is liveview streams the default or replacement for temporary assigns? if so, is there a chance they’ll add a portion of guide for streams?

6

Thanks, I’ll read the module docs as is. Sad, I can’t find any user written blog or article on this.

7

They are still relatively new and even had some problems until fairly recently. My guess is that a guide will appear in hexdocs sometime soon. I was actually surprised there wasn’t one already. If I wasn’t scrambling to find a job I would maybe take a stab at getting one started.