stream_insert update_only aka stream_update

Fixes #2690.
Relates to: https://elixirforum.com/t/add-stream-update-to-liveview-streams/68107

Work in progress, no tests yet.

Author: SteffenDE

assets/js/phoenix_live_view/dom_patch.js

@@ -125,6 +125,11 @@ export default class DOMPatch {
           }
         },
         onBeforeNodeAdded: (el) => {
+          // don't add update_only nodes if they did not already exist 
+          if(this.getStreamInsert(el)?.updateOnly && !this.streamComponentRestore[el.id]){
+            return false
+          }
+
           DOM.maintainPrivateHooks(el, el, phxViewportTop, phxViewportBottom)
           this.trackBefore("added", el)
 
@@ -278,8 +283,8 @@ export default class DOMPatch {
 
     liveSocket.time("morphdom", () => {
       this.streams.forEach(([ref, inserts, deleteIds, reset]) => {
-        inserts.forEach(([key, streamAt, limit]) => {
-          this.streamInserts[key] = {ref, streamAt, limit, reset}
+        inserts.forEach(([key, streamAt, limit, updateOnly]) => {
+          this.streamInserts[key] = {ref, streamAt, limit, reset, updateOnly}
         })
         if(reset !== undefined){
           DOM.all(container, `[${PHX_STREAM_REF}="${ref}"]`, child => {

lib/phoenix_live_view.ex

@@ -1843,6 +1843,9 @@ defmodule Phoenix.LiveView do
       here as well in order to be enforced. See `stream/4` for more information on
       limiting streams.
 
+    * `:update_only` - A boolean to only update the item in the stream. If the item does not
+      exist on the client, it will not be inserted. Defaults to `false`.
+
   ## Examples
 
   Imagine you define a stream on mount with a single item:
@@ -1892,8 +1895,9 @@ defmodule Phoenix.LiveView do
   def stream_insert(%Socket{} = socket, name, item, opts \\ []) do
     at = Keyword.get(opts, :at, -1)
     limit = Keyword.get(opts, :limit)
+    update_only = Keyword.get(opts, :update_only, false)
 
-    update_stream(socket, name, &LiveStream.insert_item(&1, item, at, limit))
+    update_stream(socket, name, &LiveStream.insert_item(&1, item, at, limit, update_only))
   end
 
   @doc """

lib/phoenix_live_view/engine.ex

@@ -84,7 +84,9 @@ defmodule Phoenix.LiveView.Comprehension do
 
   @doc false
   def __annotate__(comprehension, %Phoenix.LiveView.LiveStream{} = stream) do
-    inserts = for {id, at, _item, limit} <- stream.inserts, do: [id, at, limit]
+    inserts =
+      for {id, at, _item, limit, update_only} <- stream.inserts, do: [id, at, limit, update_only]
+
     data = [stream.ref, inserts, stream.deletes]
 
     if stream.reset? do

lib/phoenix_live_view/live_stream.ex

@@ -25,7 +25,7 @@ defmodule Phoenix.LiveView.LiveStream do
     # with manually calling stream_insert multiple times, as stream_insert prepends.
     items_list =
       for item <- items, reduce: [] do
-        items -> [{dom_id.(item), -1, item, opts[:limit]} | items]
+        items -> [{dom_id.(item), -1, item, opts[:limit], opts[:update_only]} | items]
       end
 
     %LiveStream{
@@ -64,10 +64,10 @@ defmodule Phoenix.LiveView.LiveStream do
     %{stream | deletes: [dom_id | stream.deletes]}
   end
 
-  def insert_item(%LiveStream{} = stream, item, at, limit) do
+  def insert_item(%LiveStream{} = stream, item, at, limit, update_only) do
     item_id = stream.dom_id.(item)
 
-    %{stream | inserts: [{item_id, at, item, limit} | stream.inserts]}
+    %{stream | inserts: [{item_id, at, item, limit, update_only} | stream.inserts]}
   end
 
   defimpl Enumerable, for: LiveStream do
@@ -106,7 +106,7 @@ defmodule Phoenix.LiveView.LiveStream do
     defp do_reduce(list, {:suspend, acc}, fun), do: {:suspended, acc, &do_reduce(list, &1, fun)}
     defp do_reduce([], {:cont, acc}, _fun), do: {:done, acc}
 
-    defp do_reduce([{dom_id, _at, item, _limit} | tail], {:cont, acc}, fun) do
+    defp do_reduce([{dom_id, _at, item, _limit, _update_only} | tail], {:cont, acc}, fun) do
       do_reduce(tail, fun.({dom_id, item}, acc), fun)
     end
 

lib/phoenix_live_view/test/dom.ex

@@ -502,7 +502,8 @@ defmodule Phoenix.LiveViewTest.DOM do
 
     streamInserts =
       Enum.reduce(streams, %{}, fn %{ref: ref, inserts: inserts}, acc ->
-        Enum.reduce(inserts, acc, fn [id, stream_at, limit], acc ->
+        # TODO: support update_only in LiveViewTest
+        Enum.reduce(inserts, acc, fn [id, stream_at, limit, _update_only], acc ->
           Map.put(acc, id, %{ref: ref, stream_at: stream_at, limit: limit})
         end)
       end)

test/phoenix_live_view/live_stream_test.exs

@@ -13,12 +13,20 @@ defmodule Phoenix.LiveView.LiveStreamTest do
 
   test "default dom_id" do
     stream = LiveStream.new(:users, 0, [%{id: 1}, %{id: 2}], [])
-    assert stream.inserts == [{"users-2", -1, %{id: 2}, nil}, {"users-1", -1, %{id: 1}, nil}]
+
+    assert stream.inserts == [
+             {"users-2", -1, %{id: 2}, nil, nil},
+             {"users-1", -1, %{id: 1}, nil, nil}
+           ]
   end
 
   test "custom dom_id" do
     stream = LiveStream.new(:users, 0, [%{name: "u1"}, %{name: "u2"}], dom_id: &"u-#{&1.name}")
-    assert stream.inserts == [{"u-u2", -1, %{name: "u2"}, nil}, {"u-u1", -1, %{name: "u1"}, nil}]
+
+    assert stream.inserts == [
+             {"u-u2", -1, %{name: "u2"}, nil, nil},
+             {"u-u1", -1, %{name: "u1"}, nil, nil}
+           ]
   end
 
   test "default dom_id without struct or map with :id" do