如何从JPA中的两个表中获取数据

Question

我无法使用以下查询从两个表中获取所有记录

我试过这个，但我只从一张桌子上得到结果。 我想要两个表的结果，即 client_software_param_mapping 和 client_file_configuration 具有相同的 ClientId，它是从第三个 pojo(client_software_configuration) 到第一个和第二个 pojo 的外键。

public Result showClientConfiguration() {EntityManagerFactory entityManagerFactory =                          Persistence.createEntityManagerFactory("defaultPU");
  EntityManager entityManager = entityManagerFactory.createEntityManager();

Query q=entityManager.
  createQuery("SELECT c FROM client_software_param_mapping c JOIN fetch client_file_configuration f ON c.ClientId=f.ClientId");
  List data =q.getResultList();
  return ok(Json.toJson(data));
}

第一个 pojo

@Entity
public class client_file_configuration {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;

  private String sourceFolder;
  private String sourceFile;
  private String processingFolder;
  private String processingFile;
  private String processedFolder;
  private int intervalInMin;
  private String readAfterDelay;
  private String parserClass;
  private String directoryMode;
  private String fileMode;
  private String actionMode;
  private String type;
  private String fileExpressionResolver;

  @OneToOne
  @JoinColumn(name = "ClientId")

  private client_software_configuration clientSoftwareConfiguration;

  public client_software_configuration getClientSoftwareConfiguration() {
    return clientSoftwareConfiguration;
  }

  public void setClientSoftwareConfiguration(client_software_configuration clientSoftwareConfiguration) {
    this.clientSoftwareConfiguration = clientSoftwareConfiguration;
  }
}      

第二波乔

@Entity
public class client_software_param_mapping {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;

  private String paramKey;
  private String paramValue;


  public int getId() {
    return id;
  }

  public void setId(int id) {
    this.id = id;
  }

  public String getParamKey() {
    return paramKey;
  }

  public void setParamKey(String paramKey) {
    this.paramKey = paramKey;
  }

  public String getParamValue() {
    return paramValue;
  }

  public void setParamValue(String paramValue) {
    this.paramValue = paramValue;
  }

  @ManyToOne
  @JoinColumn(name = "ClientId")

  private client_software_configuration clientSoftwareConfiguration;

  public client_software_configuration getClientSoftwareConfiguration() {
    return clientSoftwareConfiguration;
  }

  public void setClientSoftwareConfiguration(client_software_configuration clientSoftwareConfiguration) {
    this.clientSoftwareConfiguration = clientSoftwareConfiguration;
  }
}      

第三名

@Entity
public class client_software_configuration {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;

  private String url;
  private int port;
  private String endPoint;
  private String isPost;
  private String isPing;
  private String params;
  private int serialNo;

  private String dateFormat;
  private String token;
}

Answer 1

这是正确的查询，因为它返回存在于该 ClientId 处的第三个 pojo 的对象，因此它能够理解 ClientId.JPQL 的类型，从不使用表名和列名。 它总是使用实体名称及其映射的字段/属性名称。所以在这里我采用了具有 ClientId 字段的第三个 pojo 的对象。

从 client_file_configuration c,client_software_param_mapping p 中选择 c,p 其中 c.clientSoftwareConfiguration = p.clientSoftwareConfiguration