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java - Hibernate如何将主表的主键复制到子表

问题描述

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（反之亦然）。EmployeeAddress

附加信息：休眠依赖：

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

我有如下给出的Employee类和实体。Address我正在尝试在Employee实体到Address实体中生成主键。

但是，我employeeId在ADDRESS表中看到休眠总是生成为 0 （我期待它被复制）。@PrimaryKeyJoinColumn我想我在使用or时会做错@MapsId。我试图同时添加两者，或者添加其中之一，但没有运气。

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：

雇员.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;
    }

标签： javahibernatejava-8

解决方案

您需要对复制主键值的实体的关联进行建模。如果你这样做，你可以用 注释关联@MapsId。

在您的示例中，实体的主键Employee使用IDENTITY 策略生成，并且Address实体应使用相同的值。为了实现这一点，您需要对实体上的一对一关联进行建模。Address您可以使用双向或单向关联映射。

如果您更喜欢单向的，您可以使用与实体address属性相同的映射注释。Employee然后，您当然需要在address之后删除该属性；）

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 +
                '}';
    }
}

这就是Address实体。此映射的重要部分是@MapsId一对一关联的注释。

@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。如果您使用继承策略 JOINED或者如果您使用旧数据库并且需要将2 个表映射到同一个实体，则可能会出现这种情况。

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