JPA Hibernate - ManyToOne 映射 - 如果不存在则插入

Question

我有以下两个类（实体）。

人类

@Entity
@Table(name = "person")
public class Person {

  @Id
  @GeneratedValue(strategy= GenerationType.SEQUENCE, 
  generator="person_id_seq")
  @SequenceGenerator(name="person_id_seq", sequenceName="person_id_seq", 
  allocationSize=1)
  private Integer person_id;

  @ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.ALL})
  @JoinColumn(name = "location_id")
  private Location location;
}

位置类

@Entity
@Table(name = "location")
public class Location {

  @Id
  @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "location_seq_gen")
  @SequenceGenerator(name = "location_seq_gen", sequenceName = "location_id_seq", allocationSize = 1)
  @Column(name = "location_id")
  private Long id;

  @Column(name = "address_1")
  private String address1;

  @Column(name = "address_2")
  private String address2;

  @Column(name = "city")
  private String city;

  @Column(name = "state")
  private String state;

  @Column(name = "zip")
  private String zipCode;

  @Column(name = "location_source_value")
  private String locationSourceValue;

public Location() {
}

public Location(String address1, String address2, String city, String state, String zipCode) {
    this.address1 = address1;
    this.address2 = address2;
    this.city = city;
    this.state = state;
    this.zipCode = zipCode;
}

public Long getId() {
    return id;
}

public Long getId(String address1, String address2, String city, String state, String zipCode){
    return this.id;
}

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

public String getAddress1() {
    return address1;
}

public void setAddress1(String address1) {
    this.address1 = address1;
}

public String getAddress2() {
    return address2;
}

public void setAddress2(String address2) {
    this.address2 = address2;
}

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
}

public String getState() {
    return state;
}

public void setState(String state) {
    this.state = state;
}

public String getZipCode() {
    return zipCode;
}

public void setZipCode(String zipCode) {
    this.zipCode = zipCode;
}

public String getLocationSourceValue() {
    return locationSourceValue;
}

public void setLocationSourceValue(String locationSourceValue) {
    this.locationSourceValue = locationSourceValue;
}

}

我希望能够做到以下几点：

• 当我插入一个新的人员记录时，我会提供addressLine1、addressLine2、city、state、zipcode等信息，它应该在Location表中检查记录是否存在。如果存在，则从Location表获取location_id，并使用现有的location_id插入新的Person记录。如果不存在，则在Location表中创建一个新记录，获取location_id，并将其用作新的Person记录的location_id。

我相信这可以通过适当的JPA Hibernate注释实现。

目前，每当我插入一个新的Person记录时，即使Location已经存在，它也会在Location表中创建一个新的记录。

请帮忙解决。谢谢！

- coder1416

Answer 1

你是否重写了equals和hashCode方法？通过这种方法，你将为表中的每一行添加标识。你已经正确指定了注释，但Hibernate无法确定该行是否存在。在内部，Hibernate使用Map，因此equals和hashCode应该能解决你的问题。

- Sergiy Rezvan

---

谢谢您的回复。请您能否举个例子详细说明一下。 - coder1416

请查看此链接 https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/persistent-classes.html#persistent-classes-equalshashcode在这里，您可以找到为什么需要重写这些方法以及示例。 - Sergiy Rezvan

@Sergiy Rezvan 我也遇到了同样的问题，但是我并没有很清楚地理解所指定的内容。请详细说明应在实体表中进行哪些更改。 - eccentricCoder

@SergiyRezvan 感谢您指向文档，但它不够清晰。此外，我尝试了上面的示例与简单的代码 https://dzone.com/tutorials/java/hibernate/hibernate-example/hibernate-mapping-many-to-one-using-annotations-1.html。在这个例子中，如果我将其传递给构造函数，它可以工作，但是当我使用setter方法设置时它不起作用。 - coder1416

@SergiyRezvan 请帮忙。 - coder1416