Question

我有一个Spring应用程序，它从Cassandra数据库中请求数据。通常，我将在存储库类的查询方法中使用的方便的POJO指定为数据模型返回结果。

但在我目前的情况下，我不希望映射到特定的模型对象。我希望查询结果为原始JSON字符串（或Map）。

根据以下文档，我可以在CQL查询中使用JSON关键字请求原始JSON：Through Associations

理论上，Spring Data JPA应支持简单类型作为查询结果：https://docs.datastax.com/en/cql/3.3/cql/cql_using/useQueryJSON.html

@Repository public interface DataRepository extends CassandraRepository<String> {

  @Query(
     "SELECT JSON uid"
         + ", version"
         + ", timestamp"
         + ", message"
         + " FROM message_data WHERE uid=?0 ALLOW FILTERING")
  Optional<String> findById(UUID id);
}

但最后，我在Spring应用程序的启动时遇到映射错误：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'dataController' defined in URL [jar:file:/app.jar!/BOOT-INF/classes!/.../DataController.class]: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataRepository': Invocation of init method failed; nested exception is org.springframework.data.mapping.model.MappingException: Could not lookup mapping metadata for domain class java.lang.String
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:749) ~[spring-beans-4.3.13.RELEASE.jar!/:4.3.13.RELEASE]
    ...
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataRepository': Invocation of init method failed; nested exception is org.springframework.data.mapping.model.MappingException: Could not lookup mapping metadata for domain class java.lang.String
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1628) ~[spring-beans-4.3.13.RELEASE.jar!/:4.3.13.RELEASE]
    ...
Caused by: org.springframework.data.mapping.model.MappingException: Could not lookup mapping metadata for domain class java.lang.String
    at org.springframework.data.cassandra.repository.support.CassandraRepositoryFactory.getEntityInformation(CassandraRepositoryFactory.java:104) ~[spring-data-cassandra-1.5.9.RELEASE.jar!/:na]

我在这里缺少什么？

SOLUTION：

根据接受的答案，下面的代码片段做了诀窍：

import com.datastax.driver.core.querybuilder.QueryBuilder;
import com.datastax.driver.core.querybuilder.Select;

...
@Autowired
private CassandraOperations cassandraTemplate;
...

private Optional<String> findById(final UUID id) {
  final Select select = QueryBuilder.select().json().from("message_data");
  select.where(QueryBuilder.eq(...))
        .and(QueryBuilder.eq("uid", QueryBuilder.raw(id.toString())));

  return Optional.ofNullable(cassandraTemplate.selectOne(select, String.class));
}

private void insert(final MessageEntity entity) {
  cassandraTemplate.insert(entity);
}

Answer 1

DataRepository正在延长CassandraRepository<String>这是一个问题。

CassandraRepository声明就像CassandraRepository<T,ID>其中

T - the domain type the repository manages
ID - the type of the id of the entity the repository manages

在您的情况下，T将Entity/Table用于message_data表，ID将为UUID。

如果您需要运行不带存储库的查询，请使用cassandraTemplate：

@Autowired
private CassandraOperations cassandraTemplate;

带有String的CassandraRepository在查询方法中返回值

1 个答案: