java - MongoDB Java 驱动程序 @Discriminator @BsonDiscriminator 注解

Question

Mongo 文档 http://mongodb.github.io/mongo-java-driver/3.11/bson/pojos/状态:

The easiest way to enable a discriminator is to annotate the abstract class with the Discriminator annotation.

但是我现在看到的问题是，3.11 驱动程序中没有 @Discriminator 注解。我不确定它是否与 @BsonDiscriminator 相同，我可以在 https://www.javadoc.io/static/org.mongodb/mongo-java-driver/3.11.0/org/bson/codecs/pojo/annotations/package-summary.html 找到它。

我应该如何使用@Discriminator以及它在哪里？

Answer 1

这似乎是 Mongo 文档中的一个错误。我使用了@BsonDiscriminator并且它有效。

我找不到好的例子，所以我在这里发布了我实现的内容来检查这一点。请注意，我使用了 jackson ，但这没有在这个答案中显示。因此，应删除 Parent、Pojo1、Pojo2 上的一些注释:

@JsonTypeInfo(include=JsonTypeInfo.As.WRAPPER_OBJECT, use=JsonTypeInfo.Id.NAME)
@JsonSubTypes({
        @JsonSubTypes.Type(value = Pojo1.class),
        @JsonSubTypes.Type(value = Pojo2.class)})
@BsonDiscriminator
public abstract class Parent {

}

子类:

@Data
@NoArgsConstructor
public class Pojo1 extends Parent {
    String string;
    Integer number;
    Boolean flag;
}

@Data
@NoArgsConstructor
public class Pojo2 extends Parent {
    String string;
    Integer number;
    Boolean flag;
}

容器类:

@Data
@NoArgsConstructor
public class Container {
    private String name;
    private List<Parent> pojos;
}

ContainerDAO 持久保存并读取包含父对象集合的容器对象:

public class ContainerDAO {
    private static final MongoDatabase DATABASE = MongoDB.getDatabase();
    private static final MongoCollection<Container> CONTAINER_COLLECTION =
            DATABASE.getCollection("containers", Container.class);

    static {
        CONTAINER_COLLECTION.createIndex(
                Indexes.ascending("name"), new IndexOptions().unique(true));
    }

    public static void create(Container container){
        Bson filter =
                eq("name", container.getName());
        ReplaceOptions options = new ReplaceOptions().upsert(true);
        CONTAINER_COLLECTION.replaceOne(filter, container, options);
    }
    
    public static Container getByName(String name) {
        Container container = CONTAINER_COLLECTION.find(
                    eq("name", name))
                .first();
        return container;
    }

    public static void deleteOne(String name) {
        Bson filter =
                eq("name", name);
        CONTAINER_COLLECTION.deleteOne(filter);
    }
}

以及数据库连接对象:

/**
 * MongoDb database and connection settings class
 */
public class MongoDB {

    private static final MongoDatabase DATABASE; 

    static {
        
        ...

        PojoCodecProvider pojoCodecProvider = PojoCodecProvider
                .builder().register(com.researchforgood.survey.jackson.Parent.class, com.researchforgood.survey.jackson.Pojo1.class, com.researchforgood.survey.jackson.Pojo2.class).build();

        CodecRegistry pojoCodecRegistry = fromRegistries(MongoClientSettings.getDefaultCodecRegistry(),
                fromProviders(pojoCodecProvider, PojoCodecProvider.builder().automatic(true).build()));
        MongoClientSettings settings = MongoClientSettings.builder()
                .codecRegistry(pojoCodecRegistry)
                .applyConnectionString(new ConnectionString(settingsMap.get("url")))
                .build();
        MongoClient mongoClient = MongoClients.create(settings);
        DATABASE = mongoClient.getDatabase(settingsMap.get("database"));
    }
    
    public static MongoDatabase getDatabase() {
        return DATABASE;
    }

}

这里是测试 - 使用示例

@Test
public void saveAndRestorePojo() throws JsonProcessingException {
    ContainerDAO.create(container);

    Container containerFromDB = ContainerDAO.getByName(container.getName());
    LOG.info(containerFromDB.toString());

    assertEquals(containerFromDB.getPojos().get(0).getClass(), Pojo1.class);
    assertEquals(((Pojo1)containerFromDB.getPojos().get(0)).getString(), "Hello1!");
}