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ML-188: guard PubSub record updates during edit mode

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Add live_action guard to handle_info({:update, record}) in both
CollectionLive.Show and WishlistLive.Show. When the user is editing,
background worker updates are skipped and a warning toast is shown
instead of overwriting the socket. Normal show-mode updates and
mismatched-ID no-ops are unchanged.

6 tests added covering all three code paths.
This commit is contained in:
Claudio Ortolina
2026-05-19 11:38:42 +01:00
parent 2fca0bb106
commit e204e555bd
9 changed files with 236 additions and 27 deletions
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backlog/tasks/ml-188 - Fix-form-edit-background-update-race-in-Show-LiveViews.md → backlog/completed/ml-188 - Fix-form-edit-background-update-race-in-Show-LiveViews.md
+27 -11
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@@ -1,10 +1,10 @@
---
id: ML-188
title: Fix form edit + background update race in Show LiveViews
status: To Do
status: Done
assignee: []
created_date: "2026-05-19 08:42"
updated_date: "2026-05-19 09:00"
updated_date: "2026-05-19 10:18"
labels:
- audit
- bug
@@ -19,6 +19,10 @@ documentation:
modified_files:
- lib/music_library_web/live/collection_live/show.ex
- lib/music_library_web/live/wishlist_live/show.ex
- lib/music_library_web/live_helpers/record_actions.ex
- test/music_library_web/live/collection_live/show_test.exs
- test/music_library_web/live/wishlist_live/show_test.exs
- docs/architecture.md
priority: medium
ordinal: 23000
---
@@ -48,15 +52,15 @@ When a user is editing a record in a modal (`live_action == :edit`) and a backgr
<!-- AC:BEGIN -->
- [ ] #1 handle_info({:update, record}) skips assign(:record, ...) when live_action == :edit in CollectionLive.Show
- [ ] #2 handle_info({:update, record}) skips assign(:record, ...) when live_action == :edit in WishlistLive.Show
- [ ] #3 Warning toast shown to user when background update occurs during edit (different wording from normal info toast)
- [ ] #4 handle_info({:update, record}) still works normally when live_action == :show
- [ ] #5 When user navigates away from edit, handle_params re-fetches fresh record with worker changes
- [ ] #6 Mismatched record.id still handled as no-op (socket unchanged)
- [ ] #7 Tests added for all three cases: :edit guard, :show normal path, mismatched-id no-op
- [ ] #8 docs/architecture.md updated to mention live_action guard
- [ ] #9 Comment added in RecordActions.handle_record_updated/2 noting intentional bypass during :edit
- [x] #1 handle_info({:update, record}) skips assign(:record, ...) when live_action == :edit in CollectionLive.Show
- [x] #2 handle_info({:update, record}) skips assign(:record, ...) when live_action == :edit in WishlistLive.Show
- [x] #3 Warning toast shown to user when background update occurs during edit (different wording from normal info toast)
- [x] #4 handle_info({:update, record}) still works normally when live_action == :show
- [x] #5 When user navigates away from edit, handle_params re-fetches fresh record with worker changes
- [x] #6 Mismatched record.id still handled as no-op (socket unchanged)
- [x] #7 Tests added for all three cases: :edit guard, :show normal path, mismatched-id no-op
- [x] #8 docs/architecture.md updated to mention live_action guard
- [x] #9 Comment added in RecordActions.handle_record_updated/2 noting intentional bypass during :edit
<!-- AC:END -->
## Implementation Notes
@@ -117,3 +121,15 @@ Run: `mix test test/music_library_web/live/collection_live/show_test.exs test/mu
- Update `docs/architecture.md`: the existing line about `handle_info/2` validating inbound record updates against `socket.assigns.record.id` should also mention the `live_action` guard for form-edit safety
- Update the task's final summary with a brief note about the design decision
<!-- SECTION:NOTES:END -->
## Final Summary
<!-- SECTION:FINAL_SUMMARY:BEGIN -->
Added `live_action` guard to `handle_info({:update, record})` in both CollectionLive.Show and WishlistLive.Show. When the user is editing a record (`live_action == :edit`), background worker updates are skipped and a distinct warning toast ("Your edits may be stale — save and re-open...") is shown instead of silently overwriting the socket. When showing (`live_action == :show`), existing behavior is unchanged — the record updates and shows "Record updated in the background". Mismatched-ID records remain a no-op.
This prevents the race where a background worker (PopulateGenres, RefreshCover, etc.) updates the DB and broadcasts `{:update, v2}` while the user's edit modal is open with v1. The guard keeps `@record = v1` on the socket so the form saves only user-changed fields via Ecto changeset semantics. When the user navigates away from edit, `handle_params` re-fetches the fresh record with worker changes.
6 tests added (3 per LiveView), covering: `:show` normal path, `:edit` guard path, and mismatched-ID no-op. Architecture docs updated with guard description.
<!-- SECTION:FINAL_SUMMARY:END -->
docs/architecture.md
+2 -2
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@@ -251,8 +251,8 @@ HTTP 429 into `:rate_limit` vs `:auth_error` by reading the body `code`
## PubSub Topics
| PubSub | Topic Pattern | Message | Used By |
| ---------------- | -------------------------- | ------------------------ | ---------------------------------------------------------------------------------------------- |
| `:music_library` | `"records:#{id}"` | `{:update, record}` | CollectionLive.Show, WishlistLive.Show — subscribe in handle_params, unsubscribe on navigation |
| ---------------- | -------------------------- | ------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `:music_library` | `"records:#{id}"` | `{:update, record}` | CollectionLive.Show, WishlistLive.Show — subscribe in `handle_params`, unsubscribe on navigation. `handle_info({:update, record})` matches record ID against socket and guards against applying background updates during `:edit` `live_action` (skips assign, shows warning toast) to prevent worker changes from overwriting in-progress form edits |
| `:music_library` | `"records:index_changed"` | `:records_index_changed` | CollectionLive.Index, WishlistLive.Index — auto-refresh when background import completes |
| `:music_library` | `"listening_stats:update"` | `%{track_count: n}` | StatsLive.Index, ScrobbledTracksLive.Index — new scrobbles arrived |
lib/music_library_web/live/collection_live/show.ex
+15 -3
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@@ -472,13 +472,25 @@ defmodule MusicLibraryWeb.CollectionLive.Show do
@impl true
def handle_info({:update, record}, socket) do
if record.id == socket.assigns.record.id do
cond do
record.id != socket.assigns.record.id ->
{:noreply, socket}
socket.assigns.live_action == :edit ->
{:noreply,
socket
|> put_toast(
:warning,
gettext(
"Record was updated in the background. Your edits may be stale — save and re-open to see the latest data."
)
)}
true ->
{:noreply,
socket
|> RecordActions.handle_record_updated(record)
|> assign_similar_records()}
else
{:noreply, socket}
end
end
lib/music_library_web/live/wishlist_live/show.ex
+15 -3
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@@ -365,10 +365,22 @@ defmodule MusicLibraryWeb.WishlistLive.Show do
@impl true
def handle_info({:update, record}, socket) do
if record.id == socket.assigns.record.id do
{:noreply, RecordActions.handle_record_updated(socket, record)}
else
cond do
record.id != socket.assigns.record.id ->
{:noreply, socket}
socket.assigns.live_action == :edit ->
{:noreply,
socket
|> put_toast(
:warning,
gettext(
"Record was updated in the background. Your edits may be stale — save and re-open to see the latest data."
)
)}
true ->
{:noreply, RecordActions.handle_record_updated(socket, record)}
end
end
lib/music_library_web/live_helpers/record_actions.ex
+4
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@@ -119,6 +119,10 @@ defmodule MusicLibraryWeb.LiveHelpers.RecordActions do
@doc """
Handles a background record update. Returns the updated socket (not wrapped
in `{:noreply, ...}`) so the caller can pipe additional assigns.
**Note:** Callers intentionally bypass this function when `live_action == :edit`
to prevent background worker updates from overwriting the user's in-progress
form edits. See CollectionLive.Show and WishlistLive.Show `handle_info({:update, record})`.
"""
def handle_record_updated(socket, record) do
socket
priv/gettext/default.pot
+6
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@@ -2556,3 +2556,9 @@ msgstr ""
#, elixir-autogen, elixir-format
msgid "ISO format"
msgstr ""
#: lib/music_library_web/live/collection_live/show.ex
#: lib/music_library_web/live/wishlist_live/show.ex
#, elixir-autogen, elixir-format
msgid "Record was updated in the background. Your edits may be stale — save and re-open to see the latest data."
msgstr ""
priv/gettext/en/LC_MESSAGES/default.po
+6
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@@ -2556,3 +2556,9 @@ msgstr ""
#, elixir-autogen, elixir-format
msgid "ISO format"
msgstr ""
#: lib/music_library_web/live/collection_live/show.ex
#: lib/music_library_web/live/wishlist_live/show.ex
#, elixir-autogen, elixir-format
msgid "Record was updated in the background. Your edits may be stale — save and re-open to see the latest data."
msgstr ""
test/music_library_web/live/collection_live/show_test.exs
+88
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@@ -7,6 +7,7 @@ defmodule MusicLibraryWeb.CollectionLive.ShowTest do
alias MusicBrainz.Fixtures
alias MusicLibrary.Assets.Transform
alias MusicLibrary.Records.Record
alias Phoenix.PubSub
describe "Edit record from show page" do
test "can navigate to the record edit form", %{conn: conn} do
@@ -68,6 +69,93 @@ defmodule MusicLibraryWeb.CollectionLive.ShowTest do
end
end
describe "handle_info({:update, record}) with live_action guard" do
test "updates record when showing (live_action is :show)", %{conn: conn} do
record = record()
release_response = Fixtures.Release.release(:marbles)
Req.Test.stub(MusicBrainz.API, fn conn ->
Req.Test.json(conn, release_response)
end)
updated_record = %{record | title: "Background Updated Title"}
session =
conn
|> visit(~p"/collection/#{record.id}")
|> render_async()
PubSub.broadcast(
MusicLibrary.PubSub,
"records:#{record.id}",
{:update, updated_record}
)
session
|> assert_has("*", text: "Background Updated Title", timeout: 200)
|> assert_has("#toast-group", text: "Record updated in the background")
end
test "skips update when editing and shows warning toast", %{conn: conn} do
record = record()
release_response = Fixtures.Release.release(:marbles)
Req.Test.stub(MusicBrainz.API, fn conn ->
Req.Test.json(conn, release_response)
end)
updated_record = %{record | title: "Should Not Appear"}
session =
conn
|> visit(~p"/collection/#{record.id}")
|> render_async()
|> click_link("Edit")
PubSub.broadcast(
MusicLibrary.PubSub,
"records:#{record.id}",
{:update, updated_record}
)
session
|> refute_has("h2", text: "Should Not Appear")
|> assert_has(
"#toast-group",
text:
"Record was updated in the background. Your edits may be stale — save and re-open to see the latest data."
)
end
test "no-ops when broadcasted record has mismatched ID", %{conn: conn} do
record = record()
other_record = record()
release_response = Fixtures.Release.release(:marbles)
Req.Test.stub(MusicBrainz.API, fn conn ->
Req.Test.json(conn, release_response)
end)
session =
conn
|> visit(~p"/collection/#{record.id}")
|> render_async()
PubSub.broadcast(
MusicLibrary.PubSub,
"records:#{record.id}",
{:update, other_record}
)
session
|> assert_has("h2", text: escape(record.title))
|> refute_has("#toast-group", text: "Record updated in the background")
end
end
describe "Side panel" do
test "shows a record's tracks", %{conn: conn} do
record = record()
test/music_library_web/live/wishlist_live/show_test.exs
+65
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@@ -6,6 +6,7 @@ defmodule MusicLibraryWeb.WishlistLive.ShowTest do
alias MusicLibrary.Assets.Transform
alias MusicLibrary.Records.Record
alias Phoenix.PubSub
describe "Edit record from show page" do
test "can navigate to the record edit form", %{conn: conn} do
@@ -51,4 +52,68 @@ defmodule MusicLibraryWeb.WishlistLive.ShowTest do
end
end
end
describe "handle_info({:update, record}) with live_action guard" do
test "updates record when showing (live_action is :show)", %{conn: conn} do
record = record(purchased_at: nil)
updated_record = %{record | title: "Background Updated Title"}
session =
conn
|> visit(~p"/wishlist/#{record.id}")
PubSub.broadcast(
MusicLibrary.PubSub,
"records:#{record.id}",
{:update, updated_record}
)
session
|> assert_has("*", text: "Background Updated Title", timeout: 200)
|> assert_has("#toast-group", text: "Record updated in the background")
end
test "skips update when editing and shows warning toast", %{conn: conn} do
record = record(purchased_at: nil)
updated_record = %{record | title: "Should Not Appear"}
session =
conn
|> visit(~p"/wishlist/#{record.id}")
|> click_link("Edit")
PubSub.broadcast(
MusicLibrary.PubSub,
"records:#{record.id}",
{:update, updated_record}
)
session
|> refute_has("h2", text: "Should Not Appear")
|> assert_has(
"#toast-group",
text:
"Record was updated in the background. Your edits may be stale — save and re-open to see the latest data."
)
end
test "no-ops when broadcasted record has mismatched ID", %{conn: conn} do
record = record(purchased_at: nil)
other_record = record(purchased_at: nil)
session =
conn
|> visit(~p"/wishlist/#{record.id}")
PubSub.broadcast(
MusicLibrary.PubSub,
"records:#{record.id}",
{:update, other_record}
)
session
|> assert_has("h2", text: escape(record.title))
|> refute_has("#toast-group", text: "Record updated in the background")
end
end
end