Return 400 instead of 500 for row delete write failures

Row delete previously returned 500 when the write failed (for example
a constraint violation raised by a trigger or foreign key), while row
update and every other write endpoint report the same failure class as
400. Delete now matches.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GrHZSypDfMnym1tM5XJAFZ

datasette/views/row.py

@@ -742,7 +742,7 @@ class RowDeleteView(BaseView):
         try:
             await resolved.db.execute_write_fn(delete_row, request=request)
         except Exception as e:
-            return _error([str(e)], 500)
+            return _error([str(e)], 400)
 
         await self.ds.track_event(
             DeleteRowEvent(

existing-api.md

@@ -968,8 +968,8 @@ does not change the SQLite schema.
 - **Request:** no body required (any body is ignored — there is no
   confirmation step, unlike table drop).
 - **Response** — 200 `{"ok": true}`; with `?_redirect_to_table` a `redirect`
-  key is added. A failure during the write returns **500** with the message
-  (unlike update's 400). Emits `delete-row`.
+  key is added. A failure during the write returns 400 with the message,
+  matching update. Emits `delete-row`.
 
 ---
 

stable-api-recommendations.md

@@ -98,10 +98,11 @@ key — see §2.)
 
 ### 1c. Wrong-status outliers (P2)
 
-- Row **delete** write failures return **500** (views/row.py:757) while row
+- ~~Row **delete** write failures return **500** (views/row.py:757) while row
   **update** write failures return **400** (views/row.py:832-835). Same
   failure class, different status; pick 400 (or 409 for constraint
-  violations) for both.
+  violations) for both.~~ ✅ **Done** — delete now returns 400, matching
+  update and the rest of the write API.
 - Invalid or expired bearer tokens silently degrade the request to anonymous,
   so clients see a 403 permission error (or worse, anonymous-permitted data)
   rather than a 401 (tokens.py:147-193). For 1.0, a malformed/expired
@@ -337,7 +338,8 @@ Concerns:
    []}`** while `.csv` on the same request returns 400 `"?sql= is
    required"`. The JSON behavior masks caller bugs; return 400 on both.
 3. **`_shape=object` HTTP 200 error** (§1b) — almost certainly unintended.
-4. **Row delete 500** (§1c) — inconsistent with every sibling endpoint.
+4. ~~**Row delete 500** (§1c) — inconsistent with every sibling endpoint.~~
+   ✅ Done — now 400.
 5. **The "SQL Interrupted" error embeds an HTML fragment in the JSON `error`
    value** (views/database.py:805-820). Error strings in the JSON API should
    be plain text.

tests/test_error_shape.py

@@ -363,3 +363,35 @@ async def test_write_query_rejected_operation_is_canonical_403(ds_write_query):
     )
     data = assert_canonical_error(response, 403)
     assert data["redirect"] is None
+
+
+# Row delete write failures must be 400, matching row update
+
+
+@pytest.mark.asyncio
+async def test_row_delete_write_failure_is_400(tmp_path_factory):
+    db_directory = tmp_path_factory.mktemp("dbs")
+    db_path = str(db_directory / "data.db")
+    conn = sqlite3.connect(db_path)
+    conn.execute("vacuum")
+    conn.execute("create table docs (id integer primary key, title text)")
+    conn.execute("insert into docs (id, title) values (1, 'One')")
+    conn.execute(
+        "create trigger no_delete before delete on docs "
+        "begin select raise(abort, 'deletes are blocked'); end"
+    )
+    conn.commit()
+    conn.close()
+    ds = Datasette([db_path])
+    ds.root_enabled = True
+    try:
+        response = await ds.client.post(
+            "/data/docs/1/-/delete",
+            json={},
+            headers={"Content-Type": "application/json"},
+            actor={"id": "root"},
+        )
+        data = assert_canonical_error(response, 400)
+        assert "deletes are blocked" in data["error"]
+    finally:
+        ds.close()