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Mongodb java:带有泛型字段的Perist POJO类
EN

Stack Overflow用户
提问于 2018-09-06 13:34:36
回答 1查看 1.3K关注 0票数 3

我有一个POJO类,看起来像这样-

public class CacheEntity<V> {
  private String cacheId;
  private V value;

  public static final String ID_KEY = "cacheId";

  public CacheEntity() {
  }

  public CacheEntity(String cache_id, V value) {
    this.cacheId = cache_id;
    this.value = value;
  }

  public V getValue() {
    return value;
  }

  public void setValue(V value) {
    this.value = value;
  }

  public String getCacheId() {
    return cacheId;
  }

  public void setCacheId(String cacheId) {
    this.cacheId = cacheId;
  }
}

我使用的是官方驱动mongodb- driver -sync版本3.8.1

正如文档here中所提到的,我将CodecRegistry与automatic PojoCodecProvider结合使用。当我试图持久化这个实体时,我得到了以下错误。

Exception in thread "main" org.bson.codecs.configuration.CodecConfigurationException: CacheEntity contains generic types that have not been specialised.
Top level classes with generic types are not supported by the PojoCodec.
    at org.bson.codecs.pojo.PojoCodecImpl.encode(PojoCodecImpl.java:93)
    at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:63)
    at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:29)
    at com.mongodb.operation.BulkWriteBatch$WriteRequestEncoder.encode(BulkWriteBatch.java:398)
    at com.mongodb.operation.BulkWriteBatch$WriteRequestEncoder.encode(BulkWriteBatch.java:377)
    at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:63)
    at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:29)
    at com.mongodb.internal.connection.BsonWriterHelper.writeDocument(BsonWriterHelper.java:75)
    at com.mongodb.internal.connection.BsonWriterHelper.writePayload(BsonWriterHelper.java:59)
    at com.mongodb.internal.connection.CommandMessage.encodeMessageBodyWithMetadata(CommandMessage.java:143)
    at com.mongodb.internal.connection.RequestMessage.encode(RequestMessage.java:138)
    at com.mongodb.internal.connection.CommandMessage.encode(CommandMessage.java:57)
    at com.mongodb.internal.connection.InternalStreamConnection.sendAndReceive(InternalStreamConnection.java:244)
    at com.mongodb.internal.connection.UsageTrackingInternalConnection.sendAndReceive(UsageTrackingInternalConnection.java:99)
    at com.mongodb.internal.connection.DefaultConnectionPool$PooledConnection.sendAndReceive(DefaultConnectionPool.java:444)
    at com.mongodb.internal.connection.CommandProtocolImpl.execute(CommandProtocolImpl.java:72)
    at com.mongodb.internal.connection.DefaultServer$DefaultServerProtocolExecutor.execute(DefaultServer.java:200)
    at com.mongodb.internal.connection.DefaultServerConnection.executeProtocol(DefaultServerConnection.java:269)
    at com.mongodb.internal.connection.DefaultServerConnection.command(DefaultServerConnection.java:131)
    at com.mongodb.operation.MixedBulkWriteOperation.executeCommand(MixedBulkWriteOperation.java:418)
    at com.mongodb.operation.MixedBulkWriteOperation.executeBulkWriteBatch(MixedBulkWriteOperation.java:256)
    at com.mongodb.operation.MixedBulkWriteOperation.access$700(MixedBulkWriteOperation.java:67)
    at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:200)
    at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:191)
    at com.mongodb.operation.OperationHelper.withReleasableConnection(OperationHelper.java:419)
    at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:191)
    at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:67)
    at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.execute(MongoClientDelegate.java:193)
    at com.mongodb.client.internal.MongoCollectionImpl.executeSingleWriteRequest(MongoCollectionImpl.java:960)
    at com.mongodb.client.internal.MongoCollectionImpl.executeReplaceOne(MongoCollectionImpl.java:602)
    at com.mongodb.client.internal.MongoCollectionImpl.replaceOne(MongoCollectionImpl.java:578)
    at com.mongodb.client.internal.MongoCollectionImpl.replaceOne(MongoCollectionImpl.java:567)

我能做些什么来让它工作呢?谢谢。

EN

回答 1

Stack Overflow用户

发布于 2019-06-06 03:36:55

有以下几个选项可以让它工作。

通过子类化

如果你每次都用具体的泛型类型子类化,它就会起作用:

public class MyClassCacheEntity extends CacheEntity<MyClass> {}

通过使用BsonDocument + Jackson

为了避免子类化,您可以尝试将任意对象存储为BsonDocument-s,并使用Jackson序列化/反序列化它们:

public class CacheEntity<V> {
  private String cacheId;
  private BsonDocument rawValue;

  // [...]

  // sets the value
  public void withValue(T o) {
    this.rawValue = BsonDocument.parse(new ObjectMapper().writeValueAsString(o))
  }

  // recovers the value
  public T value(Class<T> clazz) {
    return new ObjectMapper().readValue(this.rawValue.toJson(), clazz);
  }
}

除非您避免使用withValue()value()方法的getters/setters约定,否则Mongo会开始抱怨同样的泛型问题。

与纯bson相同

我认为,您也可以尝试使用org.bson.codecs.pojo.PojoCodec来完成上述操作,您可以从当前的mongo编解码器注册表中创建或提取它。如果你提前知道并给它真正的类,它就不应该抱怨泛型。

票数 2
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页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接:

https://stackoverflow.com/questions/52197137

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