Stream data disappearing from liveview unexpectedly

Phoenix Forum Questions / Help
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1

I have a newly generated resource and affiliated LiveView components that are almost entirely “stock”, generated using Phoenix 1.7. What I have is a table populated by items that displays odd behavior as I’m working with the data, with table entries disappearing in the front end.

When I start it looks like this:

start
start1483×551 32.8 KB

After I edit one of those entries using the pop-up modal what I see is this:

post_edit_only_edited_item
post_edit_only_edited_item767×468 13.3 KB

If I click on the flash message to make it go away, this is what I now see:

empty_table
empty_table767×468 7.37 KB

As stated this is almost entirely “stock” generated code. This is the save function in the form_component for the Map object:

  defp save_map(socket, :edit, map_params) do
    case Maps.update_map(socket.assigns.map, map_params) do
      {:ok, map} ->
        notify_parent({:saved, map})

        {:noreply,
         socket
         |> put_flash(:info, "Map updated successfully")
         |> push_patch(to: format_url(socket.assigns.patch, map.slug))}

      {:error, %Ecto.Changeset{} = changeset} ->
        {:noreply, assign_form(socket, changeset)}
    end
  end

The handler code for the parent receiving the message is:

  def handle_info({DionysusWeb.MapLive.FormComponent, {:saved, map}}, socket) do
    {:noreply, stream_insert(socket, :maps, map)}
  end

I have no other code modifying that stream (except for delete which isn’t being used here). This seems like fairly basic functionality so I’m wondering what exactly I’m doing wrong. Why are those table rows disappearing?

2

I have encountered this same problem today.

It appears that using push_patch or <link patch={patch} causes stream entries to become an empty list.

Can you add a handle_params callback function to your Live View that does something like IO.inspect(Enum.count(socket.assigns.streams.maps))? That is what I am doing and I see the count of stream entries as “0” after the patch.

3

i have the same issue. but in my case. page renders, stream elements are also rendered, but then they disappear.

my mount sets live_action based on one field, then i have handle_params like this:

  def handle_params(params, _url, socket) do
    {:noreply, apply_action(socket, socket.assigns.live_action, params)}
  end

 defp apply_action(socket, :active, _params) do
    if connected?(socket),
      do:
        Phoenix.PubSub.subscribe(
          Yetkazuv.PubSub,
          "restaurant-#{socket.assigns.vendor_restaurant.id}"
        )

    orders = socket.assigns.vendor_restaurant |> Delivery.list_restaurant_new_orders()
    new_orders_count = Enum.count(orders)

    socket
    |> stream(:orders, orders)
    |> assign(:new_orders_count, new_orders_count)
  end
4

Make sure you have the required DOM attributes… I had this behavior too until adding the phx-update=“stream” on the parent DOM container and the DOM id on each element.
https://hexdocs.pm/phoenix_live_view/Phoenix.LiveView.html#stream/4-required-dom-attributes

5

Ran into this problem and figured out what was going wrong, at least in my case. It’s probably mentioned in the documentation somewhere, but leaving this here for when it happens to me again in a year :crazy_face:

Basically if the stream container gets removed from the DOM, it loses the entries. So if you have something like :if={@live_action == :index} or <%= if @live_action == :index %> or whatever to hide the list, you lose those entries when it gets removed from the DOM. Instead, you need to use Phoenix.LiveView.JS.hide/1,2 or class={@live_action != :index || "hidden"}.

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