Realm-C++ SDK嵌套对象Schema验证失败问题排查

尝试使用realm-cpp SDK（alpha版本）打开新的Realm数据库文件，定义了包含嵌套对象的Schema：

struct Card : realm::object<Card> {
    realm::persisted<realm::object_id> _id{realm::object_id::generate()};
    realm::persisted<std::string> name;
    realm::persisted<std::string> question;
    realm::persisted<std::vector<std::string>> options;

    static constexpr auto schema =
        realm::schema("Card",
                      realm::property<&Card::_id, true>("_id"),
                      realm::property<&Card::name>("name"),
                      realm::property<&Card::question>("question"),
                      realm::property<&Card::options>("options")
        );
  };

struct Deck : realm::object<Deck> {
    realm::persisted<realm::object_id> _id{realm::object_id::generate()};
    realm::persisted<std::string> name;
    realm::persisted<std::vector<Card>> cards;

    static constexpr auto schema =
        realm::schema("Deck",
                      realm::property<&Deck::_id, true>("_id"),
                      realm::property<&Deck::name>("name"),
                      realm::property<&Deck::cards>("cards")
        );

  };

auto realm = realm::open<Deck>({dbFile});

移除Deck结构体中的realm::persisted<std::vector<Card>> cards属性时一切正常，但添加该嵌套属性后，抛出运行时异常：

DB: 30017 Thread 0x108a6c580: Open file: ./test.db/realm.db
libc++abi: terminating with uncaught exception of type realm::SchemaValidationException: Schema validation failed due to the following errors:
- Property 'Deck.cards' of type 'array' has unknown object type 'Card'

Process finished with exit code 134 (interrupted by signal 6: SIGABRT)

环境版本：

• realm-cpp sdk alpha
• cmake 3.18.1
• macOS Monterey 12.6.5
• Apple clang version 14.0.0 (clang-1400.0.29.202). Target: arm64-apple-darwin21.6.0.

问题核心是打开数据库时仅注册了Deck类型，未注册其依赖的Card类型，导致Realm无法识别Deck.cards属性中的嵌套对象类型。

两种修复方式：

1. 在realm::open中同时指定所有关联类型

// 同时传入Deck和Card类型，让Realm加载所有依赖的Schema
auto realm = realm::open<Deck, Card>({dbFile});

2. 显式构建包含所有Schema的配置

realm::db_config config{dbFile};
// 将Deck和Card的Schema都加入配置
config.set_schema(realm::schema{Deck::schema, Card::schema});
auto realm = realm::open(std::move(config));

以上两种方式都能让Realm识别Card类型，通过Schema验证。

内容的提问来源于stack exchange，提问作者matt