在 Spring 本机查询项目中获取空值

Question

这是我的数据存储库文件，我使用本机查询来检索数据的所有数据地址（位置）。我使用 Postman 调用了该函数，但得到了位置的空输出。第一次使用Native query 真的无法解决这些错误

DataRepository

public interface DataRepository extends JpaRepository<Data, Long> {

    @Query(value = "SELECT dataAddress FROM Data")
    List<DataProject> getDataAddress();
}

DataServiceImpl

    public List<DataProject> getDataAddress() {
        return dataRepository.getDataAddress();
    }

数据服务

List<DataProject> getDataAddress();

DataModel

@Entity
@Table(name = "CCCData")
public class Data {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long dataId;

    @Column(name = "DATA_NAME")
    private String dataName;

    @Column(name ="DATA_ADDRESS")
    private String dataAddress;

    @Column(name = "DATA_DESC")
    private String dataDesc;

    @CreationTimestamp
    private Date dateOfCreated;

    @CreationTimestamp
    private Date dateOfUpdated;

    public long getDataId() {
        return dataId;
    }

    public void setDataId(long dataId) {
        this.dataId = dataId;
    }

    public String getDataName() {
        return dataName;
    }

    public void setDataName(String dataName) {
        this.dataName = dataName;
    }

    public String getDataAddress() {
        return dataAddress;
    }

    public void setDataAddress(String dataAddress) {
        this.dataAddress = dataAddress;
    }

    public String getDataDesc() {
        return dataDesc;
    }

    public void setDataDesc(String dataDesc) {
        this.dataDesc = dataDesc;
    }

    public Date getDateOfCreated() {
        return dateOfCreated;
    }

    public void setDateOfCreated(Date dateOfCreated) {
        this.dateOfCreated = dateOfCreated;
    }

    public Date getDateOfUpdated() {
        return dateOfUpdated;
    }

    public void setDateOfUpdated(Date dateOfUpdated) {
        this.dateOfUpdated = dateOfUpdated;
    }

DataProjection

public interface DataProject {

    String getDataAddress();
}

数据控制器

@GetMapping("/data/locations")
    public List<DataProject> getDataAddress() {
        return dataService.getDataAddress();
    }

邮差输出

[
    {
        "dataAddress": null
    },
    {
        "dataAddress": null
    },
    {
        "dataAddress": null
    },
    {
        "dataAddress": null
    }
]

Answer 1

Spring 不会 return 您只能使用以下查询来解决。它仍然return你DATA对象

public interface DataRepository extends JpaRepository<Data, Long> {

    @Query(value = "SELECT dataAddress FROM Data")
    List<DataProject> getDataAddress();
}

为了仅获取 DataAddress，您需要在 Data 模型中创建一个构造函数，仅用于 DataAddress

public Data(String dataAddress) {
    this.dataAddress = dataAddress;
}

您的查询将如下所示：

public interface DataRepository extends JpaRepository<Data, Long> {

    @Query(value = "SELECT new Data(dataAddress) FROM Data")
    List<DataProject> getDataAddress();
}

更新 1：

如果您需要将此用于具有相同数据类型的其他字段，那么基于 'constructor' 以上的方法将失败。还有一些其他选择：

You can fetch DATA object and use java stream map function to extract only 1 field. data.stream().map((data) -> data.getDataAddress()).collect(Collectors.toList())

You can use native SQL query to fetch only required fields.
@Query(value = "SELECT d.data_address FROM CCCData d", nativeQuery=true)

在 Spring 本机查询项目中获取空值

Getting Null Values in Spring Native Query Project

spring-boot

postman

nativequery