Question

当我尝试从我的dynamoDB表中查询数据时，我得到一个空对象引用错误：

 mapper = new DynamoDBMapper(ddbClient);

 DataMapperClass dataMapperClass = new DataMapperClass();
 dataMapperClass.setHash("theHashValueIset");

 String queryString = String.valueOf("theRangeValueIset");

 Condition rangeKeyCondition = new Condition()
     .withComparisonOperator(ComparisonOperator.BEGINS_WITH.toString())
     .withAttributeValueList(new AttributeValue().withS(queryString.toString()));

 DynamoDBQueryExpression <DataMapperClass> queryExpression = new DynamoDBQueryExpression<DataMapperClass>()
     .withHashKeyValues(dataMapperClass)
     .withRangeKeyCondition("rangeAttributeOnTable", rangeKeyCondition)
     .withConsistentRead(false);

 PaginatedQueryList<DataMapperClass> result = mapper.query(DataMapperClass.class, queryExpression);

我的DataMapperClass.class：

  @DynamoDBTable(tableName = "myTableName")
  public class DataMapperClass {

  private String hash;//based on a set of categories I chose
  private String objectID; //auto generated 


  //Hash
  @DynamoDBHashKey(attributeName = "hashNameOnMyTable")
  public String getHash() { return hash; }
  public void setHash(String hash) { this.hash = hash;}


  //ObjectID
  @DynamoDBRangeKey(attributeName = "rangeAttributeOnTable")
  @DynamoDBAutoGeneratedKey
  public String getObjectID() {return objectID;}
  public void setObjectID(String objectID) { this.objectID = objectID;  }

  /* other @DynamoDBAttribute*/

  }

我如何解决这个错误，我得到了＃34; PaginatedQueryList＆＃34;代码行：

Attempt to invoke interface method 'com.amazonaws.services.dynamodbv2.model.QueryResult com.amazonaws.services.dynamodbv2.AmazonDynamoDB.query(com.amazonaws.services.dynamodbv2.model.QueryRequest)' on a null object reference

Answer 1

问题解决了！

我意识到我没有在onCreate（）中执行此操作：

   ddbClient = new AmazonDynamoDBClient(identityManager.getCredentialsProvider());

DynamoDB PaginatedQueryList null对象引用错误

1 个答案: