java - CassandraRepository 在查询方法中使用字符串返回值

Question

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

但在我当前的情况下，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 等)。

根据以下文档，我可以通过在 CQL 查询中使用 JSON 关键字来请求原始 JSON:https://docs.datastax.com/en/cql/3.3/cql/cql_using/useQueryJSON.html

理论上，Spring Data JPA应该支持简单类型作为查询结果:https://www.petrikainulainen.net/programming/spring-framework/spring-data-jpa-tutorial-introduction-to-query-methods/

@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？

解决方案:

根据接受的答案，以下代码片段成功了:

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

您的DataRepository正在扩展CassandraRepository<String>这是一个问题。

CassandraRepository声明如下 CassandraRepository<T,ID>哪里

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

就您而言T将是Entity/Table您正在使用的类 message_data表和ID将是UUID .

如果您需要在没有存储库的情况下运行查询，请使用cassandraTemplate :

@Autowired
private CassandraOperations cassandraTemplate;