ML-174: research and plan

2026-05-09 19:06:29 +01:00
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+---
+id: doc-16
+title: "Research: Add menu action to empty a set"
+type: specification
+created_date: "2026-05-09 17:58"
+---
+
+# Research: Add menu action to empty a set
+
+## Current state
+
+Both the index (`RecordSetLive.Index`) and show (`RecordSetLive.Show`) views have a dropdown menu on each set with two actions:
+
+- **Edit** — `dropdown_link` that patches to the edit form
+- **Delete** — `dropdown_button` with `phx-click="delete_set"` and a `data-confirm` prompt
+
+The `RecordSets` context currently provides `remove_record_from_set/2` for removing individual records, and `delete_record_set/1` for deleting the entire set (including its items via the `has_many` association's `on_delete` behavior). There is no function to remove all items from a set while keeping the set itself.
+
+## Approach
+
+Since the user has confirmed this is a straightforward feature, there's a single clear implementation route:
+
+### 1. Context: Add `empty_record_set/1`
+
+Add a new function to `MusicLibrary.RecordSets` that deletes all `RecordSetItem` rows for a given set in a single DELETE query, then returns the reloaded (now empty) record set. This avoids N+1 deletion and keeps the set metadata intact.
+
+### 2. UI: Add "Empty" action to both dropdowns
+
+In both `index.ex` and `show.ex`, add a new `dropdown_button` with:
+
+- Text: `gettext("Empty")`
+- `phx-click="empty_set"`
+- `data-confirm` for safety: `gettext("Remove all records from this set?")`
+
+And add the corresponding `handle_event("empty_set", ...)` handler in each LiveView.
+
+### 3. Tests
+
+- Unit test for `RecordSets.empty_record_set/1`
+- LiveView test for the "empty_set" event in the index view
+- LiveView test for the "empty_set" event in the show view
+
+## Architecture impact
+
+| Touchpoint                                | Impact                                                              |
+| ----------------------------------------- | ------------------------------------------------------------------- |
+| `MusicLibrary.RecordSets`                 | New public function `empty_record_set/1`                            |
+| `MusicLibraryWeb.RecordSetLive.Index`     | New event handler + dropdown button                                 |
+| `MusicLibraryWeb.RecordSetLive.Show`      | New event handler + dropdown button                                 |
+| No schema changes needed                  | `RecordSetItem` already has `on_delete: :delete_all` via `has_many` |
+| No PubSub / routes / external API changes | This is purely local                                                |
+
+## Performance
+
+The implementation uses a single `DELETE FROM record_set_items WHERE record_set_id = ?` query (bulk delete). No N+1 risk. The reload is a single `get_record_set!/1` call that preloads the (now empty) items list. This is the same pattern already used by `delete_record_set/1` (which relies on cascading deletes) and `remove_record_from_set/2` (which deletes one item and reloads).
+
+## Documentation updates
+
+- `docs/architecture.md` — no changes needed (no new modules, schemas, or subsystems)
+- `docs/project-conventions.md` — no changes needed (follows existing patterns)