fix(mongo): fail update/delete when 0 documents match

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- **Mongo 0-match write (#776)** — `updateOne` / `replaceOne` / `deleteOne` throw when `nMatched` / `nRemoved` is 0 (wrong `_id` type, deleted doc). Inspector and JSON editor surface Save Failed instead of a success toast. An identical `$set` (`nModified == 0`) still counts as a match.
 - **Mongo full-document Save (#778)** — JSON editor Save uses `replaceOne` (whole document, `_id` locked) instead of `$set`, so fields deleted in JSON — including nested keys — are removed on the server.
 - **Mongo document editor Back (#782)** — Dirty JSON in `MongoDocumentEditor` is registered with `UnsavedWorkRegistry`. Breadcrumb Back, Home, Close, and tree navigation confirm before discarding; Cancel keeps the editor.
 - **Mongo JSON filter ObjectId / DateTime (#783)** — Document list filter parses Extended JSON (`$oid`, `$date`) and wraps a 24-character hex `_id` as `ObjectId`. A leftover string `_id` with zero matches shows how to write `{ "_id": { "$oid": "…" } }`.

lib/core/database/mongodb_service.dart

@@ -3,6 +3,31 @@ import 'package:mongo_dart/mongo_dart.dart';
 import '../storage/local_db.dart';
 import 'mongodb_connection.dart';
 
+/// Throws if a single-document write matched nothing (wrong `_id` type,
+/// concurrent delete). Same class of lie as 0-row SQL DML.
+///
+/// [nModified] is ignored: an identical `$set` still matched the document.
+void expectMongoDocumentMatched(int matched, {required String operation}) {
+  if (matched >= 1) return;
+  throw StateError(
+    '$operation failed: matched 0 documents. '
+    'The document may have been deleted or the _id type does not match.',
+  );
+}
+
+void _throwIfMongoWriteFailed(
+  WriteResult result, {
+  required String operation,
+  required int matched,
+}) {
+  if (result.hasWriteErrors) {
+    throw StateError(
+      '$operation failed: ${result.writeError?.errmsg ?? 'write error'}',
+    );
+  }
+  expectMongoDocumentMatched(matched, operation: operation);
+}
+
 /// Service for managing MongoDB connections.
 class MongoService {
   MongoService._();
@@ -241,7 +266,12 @@ class MongoService {
   ) async {
     return _withDb(connection, database, (db) async {
       final coll = db.collection(collection);
-      await coll.updateOne(filter, update);
+      final result = await coll.updateOne(filter, update);
+      _throwIfMongoWriteFailed(
+        result,
+        operation: 'updateOne',
+        matched: result.nMatched,
+      );
     });
   }
 
@@ -255,7 +285,12 @@ class MongoService {
   ) async {
     return _withDb(connection, database, (db) async {
       final coll = db.collection(collection);
-      await coll.replaceOne(filter, replacement);
+      final result = await coll.replaceOne(filter, replacement);
+      _throwIfMongoWriteFailed(
+        result,
+        operation: 'replaceOne',
+        matched: result.nMatched,
+      );
     });
   }
 
@@ -268,7 +303,12 @@ class MongoService {
   ) async {
     return _withDb(connection, database, (db) async {
       final coll = db.collection(collection);
-      await coll.deleteOne(filter);
+      final result = await coll.deleteOne(filter);
+      _throwIfMongoWriteFailed(
+        result,
+        operation: 'deleteOne',
+        matched: result.nRemoved,
+      );
     });
   }
 

test/core/database/mongo_service_test.dart

@@ -3,6 +3,31 @@ import 'package:querya_desktop/core/database/mongodb_service.dart';
 import 'package:querya_desktop/core/storage/local_db.dart';
 
 void main() {
+  group('expectMongoDocumentMatched', () {
+    test('allows 1+ matched documents', () {
+      expectMongoDocumentMatched(1, operation: 'updateOne');
+      expectMongoDocumentMatched(2, operation: 'replaceOne');
+    });
+
+    test('throws on 0 matches so Save is a failure', () {
+      expect(
+        () => expectMongoDocumentMatched(0, operation: 'updateOne'),
+        throwsA(
+          isA<StateError>().having(
+            (e) => e.message,
+            'message',
+            contains('matched 0 documents'),
+          ),
+        ),
+      );
+    });
+
+    test('nModified 0 is not a failure when the filter matched', () {
+      // Identical $set: nMatched=1, nModified=0 — still a successful save.
+      expectMongoDocumentMatched(1, operation: 'updateOne');
+    });
+  });
+
   group('MongoService.createConnection', () {
     test('creates MongoConnection from ConnectionRow', () {
       const row = ConnectionRow(