Spring Data JPA 存储库 findAll() 空指针

Question

我有一个 Spring-Boot API，其端点如下。它在 Spring Data JPA

findAll

查询上抛出空指针异常；当我注释掉这一行时，我没有收到任何错误。看来我从存储库查询中得到了空结果，但我知道数据是通过直接查询数据库而存在的。我不明白为什么我得到

topicsLookup

变量为空...任何人都可以指出我正确的方向吗？

资源：

@RequestMapping(value = "/lectures/{lectureId}",
        method = RequestMethod.GET,
        produces = MediaType.APPLICATION_JSON_VALUE)
public Map<String, SpeakerTopicLectures> getLecture(@PathVariable Long lectureId){

        Long requestReceived = new Date().getTime();
        Map<String, SpeakerTopicLectures> result = new HashMap<>();

        log.debug("** GET Request to getLecture");
        log.debug("Querying results");

        List<SpeakerTopicLectures> dataRows = speakerTopicLecturesRepository.findBySpeakerTopicLecturesPk_LectureId(lectureId);

        // This line throws the error
        List<SpeakerTopic> topicsLookup = speakerTopicsRepository.findAll();

        // Do stuff here...

        log.debug("Got {} rows", dataRows.size());
        log.debug("Request took {}ms **", (new Date().getTime() - requestReceived));

        // wrap lecture in map object
        result.put("content", dataRows.get(0));

        return result;
}

Java Bean：

@Entity
@Table(name = "speaker_topics")
@JsonInclude(JsonInclude.Include.NON_NULL)
@Data
public class SpeakerTopic implements Serializable {

    @Id
    @Column(name = "topic_id")
    private Long topicId;

    @Column(name = "topic_nm")
    private String topicName;

    @Column(name = "topic_desc")
    private String topicDesc;

    @Column(name = "topic_acm_relt_rsce")
    private String relatedResources;

}

存储库：

import org.acm.dl.api.domain.SpeakerTopic;
import org.springframework.data.jpa.repository.JpaRepository;

public interface SpeakerTopicsRepository extends JpaRepository<SpeakerTopic,Long> {

}

Answer 1

最可能的原因是

speakerTopicsRepository

本身为空，这可能是由于忘记自动装配它而导致的，例如

public class YourController {

  @Autowired private SpeakerTopicsRepository speakerTopicsRepository;

  @RequestMapping(value = "/lectures/{lectureId}",method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
  public Map<String, SpeakerTopicLectures> getLecture(@PathVariable Long lectureId) {
     // your method...
  }

}

Answer 2

存储库未在您的控制器中自动连接。

Answer 3

尝试使用

@Repository
@Transactional
public interface SpeakerTopicsRepository extends JpaRepository<SpeakerTopic,Long> {
    // Your Repository Code 
}

我认为

@Repository

和

@Transactional

不见了。请使用它。

Answer 4

我缺少@Autowired。

Answer 5

在控制器中使用@Autowire 解决了我的问题。