Write Data to a Synced Realm - C++ SDK

App Services 구성

Based on the above example object model, Device Sync is configured with the following queryable fields:

• _id (항상 포함)

• complexity

• ownerId

App Services App에는 사용자가 자신의 데이터만 읽고 쓸 수 있도록 구성된 권한이 있습니다.

{
   "roles": [
      {
         "name": "readOwnWriteOwn",
         "apply_when": {},
         "document_filters": {
            "write": {
               "ownerId": "%%user.id"
            },
            "read": {
               "ownerId": "%%user.id"
            }
         },
         "read": true,
         "write": true,
         "insert": true,
         "delete": true,
         "search": true
      }
   ]
}

ownerId 이(가) 로그인한 사용자의 user.identifier() 와(과) 일치하지 않는 Atlas collection 객체는 이 영역과 동기화할 수 없습니다.

클라이언트 Realm 데이터 모델 및 구성

The examples on this page use the following synced realm configuration with this sync query and object model:

auto appConfig = realm::App::configuration();
appConfig.app_id = APP_ID;
auto app = realm::App(appConfig);
auto user = app.login(realm::App::credentials::anonymous()).get();
auto dbConfig = user.flexible_sync_configuration();
auto syncRealm = realm::db(dbConfig);
// Add subscription
auto subscriptionUpdateSuccess =
    syncRealm.subscriptions()
        .update([](realm::mutable_sync_subscription_set &subs) {
          // Get Items from Atlas that match this query.
          // Uses the queryable field `complexity`.
          // Sync Item objects with complexity less than or equal to 4.
          subs.add<realm::Item>(
              "simple items", [](auto &obj) { return obj.complexity <= 4; });
        })
        .get();

struct Item {
  realm::primary_key<realm::object_id> _id{realm::object_id::generate()};
  std::string ownerId;
  std::string itemName;
  int64_t complexity;
};
REALM_SCHEMA(Item, _id, ownerId, itemName, complexity)

With this Sync query, any object in the Atlas collection where the complexity property's value is greater than 4 cannot sync to this realm.

성공적인 쓰기

When the write matches both user permissions 개인정보 정책에 the query subscription in the client, the Realm C++ SDK can successfully write the object to the synced realm. This object syncs with the App Services backend when the device has a network connection.

// Per the Device Sync permissions, users can only read and write data
// where the `Item.ownerId` property matches their own user ID.
auto simpleItem =
    realm::Item{.ownerId = user.identifier(),
                          .itemName = "This item meets sync criteria",
                          .complexity = 3};
// `simpleItem` successfully writes to the realm and syncs to Atlas
// because its data matches the subscription query (complexity <= 4)
// and its `ownerId` field matches the user ID.
syncRealm.write([&] { syncRealm.add(std::move(simpleItem)); });

쓰기 보상

When the write doesn't match either the query subscription or user permissions, Realm reverts the write and provides an array of compensating_write_error_info objects.

좀 더 구체적으로 말하자면, 쿼리 구독의 범위를 벗어나거나 사용자의 권한과 일치하지 않는 데이터를 쓰면 다음과 같은 상황이 발생합니다.

1. 클라이언트 영역에는 '불법적인' 쓰기에 대한 개념이 없으므로 Realm이 App Services 백엔드로 변경 집합을 해결할 때까지 처음에는 쓰기가 성공합니다.

2. 동기화되면 서버는 규칙과 권한을 적용합니다. 서버는 사용자에게 쓰기를 수행할 수 있는 권한 부여가 없다고 판단합니다.

3. 서버는 "보상 쓰기(compensating write)"라고 하는 되돌리기 작업을 클라이언트에 다시 보냅니다.

4. 클라이언트의 영역이 잘못된 쓰기 작업을 되돌립니다.

해당 객체에 대한 불법적인 쓰기와 해당 보상 쓰기 사이에 지정된 객체에 대한 모든 클라이언트 사이드 쓰기는 손실됩니다. 실제로 이는 쓰기가 성공한 것처럼 보일 수 있지만 Realm이 App Services 백엔드와 동기화되고 보상 쓰기를 수행하면 객체가 '사라집니다'.

When this occurs, you can refer to the App Services logs or use the compensating_writes_info() function in the client to get additional information on the error. For more information, refer to the 쓰기 오류 정보 보상 section on this page.

// The complexity of this item is `7`. This is outside the bounds
// of the subscription query, which triggers a compensating write.
auto complexItem =
    realm::Item{._id = primaryKey,
                          .ownerId = user.identifier(),
                          .itemName = "Test compensating writes",
                          .complexity = 7};
// This should trigger a compensating write error when it tries to sync
// due to server-side permissions, which gets logged with the error handler.
syncRealm.write([&] { syncRealm.add(std::move(complexItem)); });

Connection[2]: Session[10]: Received: ERROR "Client attempted a write that is not allowed; it has been reverted" (error_code=231, is_fatal=false, error_action=Warning)

Error:
Client attempted a write that is not allowed; it has been reverted (ProtocolErrorCode=231)
Details:
{
   "Item": {
      "ObjectID(\"6557ddb0bf050934870ca0f5\")": "write to ObjectID(\"6557ddb0bf050934870ca0f5\")
      in table \"Item\" not allowed; object is outside of
      the current query view"
   }
}

// The `ownerId` of this item does not match the user ID of the logged-in
// user. The user does not have permissions to make this write, which
// triggers a compensating write.
auto itemWithWrongOwner = realm::Item{
    .ownerId = "not the current user",
    .itemName = "Trigger an incorrect permissions compensating write",
    .complexity = 1};
syncRealm.write([&] { syncRealm.add(std::move(itemWithWrongOwner)); });

Connection[2]: Session[11]: Received: ERROR "Client attempted a write that is not allowed; it has been reverted" (error_code=231, is_fatal=false, error_action=Warning)

Error:
Client attempted a write that is outside of permissions or query filters; it has been reverted (ProtocolErrorCode=231)
Details:
{
   "Item": {
      "ObjectID(\"6557ddbabf050934870ca0f8\")": "write to ObjectID(\"6557ddbabf050934870ca0f8\")
      in table \"Item\" was denied by write filter in role \"readOwnWriteOwn\""
   }
}

auto info = receivedSyncError.compensating_writes_info();
for (auto &v : info) {
  std::cout << "A write was rejected with a compensating write error.\n";
  std::cout << "An object of type " << v.object_name << "\n";
  std::cout << "was rejected because " << v.reason << ".\n";
}

A write was rejected with a compensating write error.
An object of type Item
was rejected because write to ObjectID("6557ddb0bf050934870ca0f5") in
table "Item" not allowed; object is outside of the current query view.