java - 如何在Hibernate中将主键从主表复制到子表

Question

如何在 Hibernate 中将主键(共享键)从主表复制到子表。我正在尝试进行单向映射(Employee 引用了Address，反之亦然)。

附加信息: hibernate 依赖:

<dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-core</artifactId>
      <version>5.4.1.Final</version>
</dependency>

我有 Employee 类和 Address 实体，如下所示。我正在尝试在 Employee 实体中生成主键到 Address 实体。

但是，我看到 ADDRESS 表中的 employeeId 始终由 hibernate 生成为 0(我希望复制它)。我想我在使用 @PrimaryKeyJoinColumn 或 @MapsId 时会做错。我尝试过添加两者，或者添加其中之一，但没有成功。

以下是对应表的架构:

create table EMPLOYEE(
EMPLOYEE_ID int auto_increment,
NAME varchar(100),
SALARY double,
primary key(EMPLOYEE_ID)
);



create table ADDRESS
(
EMPLOYEE_ID int references EMPLOYEE.EMPLOYEE_ID,
STREET_NAME varchar(40),
CITY_NAME varchar(40),
STATE_NAME varchar(40),
ZIP_CODE varchar(40),
primary key(EMPLOYEE_ID)
);

实体映射如下所示:

员工.java

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.MapsId;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;
import java.io.Serializable;

@Entity
@Table(name = "EMPLOYEE")
public class Employee implements Serializable {

    @Id
    @Column(name = "EMPLOYEE_ID")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

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

    @Column(name = "SALARY")
    private double salary;

    @OneToOne
    @JoinColumn(name="EMPLOYEE_ID")
   @MapsId
    //@PrimaryKeyJoinColumn
    private Address address;

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public Employee setName(String name) {
        this.name = name;
        return this;
    }

    public double getSalary() {
        return salary;
    }

    public Employee setSalary(double salary) {
        this.salary = salary;
        return this;
    }

    public Address getAddress() {
        return address;
    }

    public Employee setAddress(Address address) {
        this.address = address;
        return this;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", salary=" + salary +
                ", address=" + address +
                '}';
    }
}

地址.java

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MapsId;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;
import java.io.Serializable;

@Entity
@Table(name = "ADDRESS")
public class Address implements Serializable {

    @Id
    @Column(name = "EMPLOYEE_ID")
    private int id;

    @Column(name = "STREET_NAME")
    private String streetName;

    @Column(name = "CITY_NAME")
    private String cityName;

    @Column(name = "STATE_NAME")
    private String stateName;

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

    public int getId() {
        return id;
    }

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

    public String getStreetName() {
        return streetName;
    }

    public Address setStreetName(String streetName) {
        this.streetName = streetName;
        return this;
    }

    public String getCityName() {
        return cityName;
    }

    public Address setCityName(String cityName) {
        this.cityName = cityName;
        return this;
    }

    public String getStateName() {
        return stateName;
    }

    public Address setStateName(String stateName) {
        this.stateName = stateName;
        return this;
    }

    public String getZipCode() {
        return zipCode;
    }

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

    @Override
    public String toString() {
        return "Address{" +
                "id=" + id +
                ", streetName='" + streetName + '\'' +
                ", cityName='" + cityName + '\'' +
                ", stateName='" + stateName + '\'' +
                ", zipCode='" + zipCode + '\'' +
                '}';
    }
}

保存方法:

  public Employee save(Employee employee){

        Session session = HibernateUtil.buildSessionFactory().openSession();
        Transaction transaction = session.beginTransaction();
        session.save(address); // Should I do this?            
        session.save(employee);
        transaction.commit();
        return employee;
    }

Answer 1

您需要在复制主键值的实体上对关联进行建模。如果这样做，您可以使用 @MapsId 注释关联。

在您的示例中，Employee 实体的主键是使用 IDENTITY strategy 生成的。 ，并且 Address 实体应使用相同的值。为了实现这一点，您需要对 one-to-one association 进行建模在 Address 实体上。您可以使用双向或单向关联映射。

如果您更喜欢单向注释，则可以使用与 Employee 实体的 address 属性相同的映射注释。当然，之后您需要删除 address 属性;)

在双向映射中，您的 Employee 实体将如下所示:

@Entity
@Table(name = "EMPLOYEE")
public class Employee implements Serializable {

    @Id
    @Column(name = "EMPLOYEE_ID")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

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

    @Column(name = "SALARY")
    private double salary;

    @OneToOne
    @JoinColumn(name="EMPLOYEE_ID")
    private Address address;

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public Employee setName(String name) {
        this.name = name;
        return this;
    }

    public double getSalary() {
        return salary;
    }

    public Employee setSalary(double salary) {
        this.salary = salary;
        return this;
    }

    public Address getAddress() {
        return address;
    }

    public Employee setAddress(Address address) {
        this.address = address;
        return this;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", salary=" + salary +
                ", address=" + address +
                '}';
    }
}

这是Address 实体。此映射的重要部分是一对一关联上的 @MapsId 注释。

@Entity
@Table(name = "ADDRESS")
public class Address implements Serializable {

    @Id
    @Column(name = "EMPLOYEE_ID")
    private int id;

    @Column(name = "STREET_NAME")
    private String streetName;

    @Column(name = "CITY_NAME")
    private String cityName;

    @Column(name = "STATE_NAME")
    private String stateName;

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

    @OneToOne(mappedBy="address")
    @MapsId
    private Employee employee

    public int getId() {
        return id;
    }

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

    public String getStreetName() {
        return streetName;
    }

    public Address setStreetName(String streetName) {
        this.streetName = streetName;
        return this;
    }

    public String getCityName() {
        return cityName;
    }

    public Address setCityName(String cityName) {
        this.cityName = cityName;
        return this;
    }

    public String getStateName() {
        return stateName;
    }

    public Address setStateName(String stateName) {
        this.stateName = stateName;
        return this;
    }

    public String getZipCode() {
        return zipCode;
    }

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

    public Employee getEmployee() {
        return employee;
    }

    public void setEmployee(Employee emp) {
        this.employee = emp;
    }

    @Override
    public String toString() {
        return "Address{" +
                "id=" + id +
                ", streetName='" + streetName + '\'' +
                ", cityName='" + cityName + '\'' +
                ", stateName='" + stateName + '\'' +
                ", zipCode='" + zipCode + '\'' +
                '}';
    }
}

如您所见，我删除了 @PrimaryKeyJoinColumn 注释。仅当您的实体映射到 2 个数据库表时才使用它。如果您使用inheritance strategy JOINED，可能会出现这种情况或者如果您使用旧数据库并需要 map 2 tables to the same entity .