JPA:从另一个表加载值列表

时间:2015-08-10 07:04:01

标签: java jpa entity-relationship

我有两张桌子vehiclevehicle_image。车辆表包含车辆的所有主数据,vehicle_image表包含图像的元信息和图像的Base64编码的字符串。在车辆上可能有0或更多图像。

现在,当我查询车辆对象时,我希望该对象包含来自vehicle_image表的信息。

我对JPA很新,我能找到的例子似乎总是从另一个表中读取一个值,而不是列表。

将属性添加到包含图像数据的车辆对象的最简单方法是什么?

@Entity
@XmlRootElement(name = "vehicle")
public class Vehicle {
  @Id
  private String vin;
  private String commission;
  @Column(name="swiss_type_number")
  private String swissTypeNumber;
  @Column(name="sale_type")
  private String saleType;
  @Column(name="exterior_color")
  private String exteriorColor;
  @Column(name="interior_color")
  private String interiorColor;
  private String remarks;
  @Column(name="additional_title")
  private String additionalTitle;
  @Column(name="added_value_description")
  private String addedValueDescription;
  @Column(name="first_registration")
  private String firstRegistration;
  private String guaranty; 
  @Column(name="last_inspection")
  private String lastInspection;

  private int dealer;
  private int mileage;
  private int price;
  private int seats;
  @Column(name="model_year")
  private int modelYear;

  @Column(name="car_damaged_in_accident")
  private boolean carDamagedInAccident;
  private boolean imported;

  // List of images
  List<VehicleImage> vehicleImages; // Something like this would be nice
}

2 个答案:

答案 0 :(得分:1)

您在此处拥有one-to-may关系,您可以使用:

@OneToMany
List<VehicleImage> vehicleImages;

参考javadoc获取它可能采用的属性,并根据您的表定义添加它们。

Here你可以找到一些如何使用它的例子。

答案 1 :(得分:1)

JPA支持实体之间的关联。你需要的是@OneToMany 如果您的vehicle_image' table contains column vehicle_id you will need following mapping in车辆类:

@Entity
@Table(name = "VEHICLE")
@XmlRootElement(name = "vehicle")
public class Vehicle {

    // other fields here

    @OneToMany(mappedBy = "vehicle")
    Set<VehicleImage> vehicleImages;

}

此问题也在VehicleImage

@Entity
@Table(name = "VEHICLE_IMAGE")
public class VehicleImage{

    // other fields here

    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.PERSIST)
    @JoinColumn(name="VEHICLE_ID", referencedColumnName = "ID")
    Vehicle vehicle;

}

另外,您应该更好地使用Set进行JPA中的集合映射,但这是一个不同的主题