jpa继承

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aoerqilengbai 2021-09-08 09:14:12 ©著作权

文章标签 jpa继承 java mysql 父类数据库 文章分类 Java 后端开发

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JPA通过在父类增加@Inheritance(strategy=InheritanceType.xxx)来声明继承关系。A支持3种继承策略：

单表继承（InheritanceType.SINGLETABLE），所有继承树上的类共用一张表，在父类指定（@DiscriminatorColumn）声明并在每个类指定@DiscriminatorValue来区分类型。
类表继承（InheritanceType.JOINED），父子类共同的部分公用一张表，其余部分保存到各自的表，通过join进行关联。

具体表继承（InheritanceType.TABLEPERCLASS)，每个具体类映射到自己的表。

下面是例子：

package com.demo.beans;

import java.util.List;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.ElementCollection;
import javax.persistence.Entity;
import javax.persistence.EntityListeners;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;

@Entity
@EntityListeners(MyMonitor.class)
public class Employee {
@Id
private int employeeId;

private String employeeName;

@ElementCollection
private Set<String> nickName;

@OneToMany(mappedBy="employee", cascade=CascadeType.ALL)
private List<Phone> phones;

public int getEmployeeId() {
return employeeId;
}

public void setEmployeeId(int employeeId) {
this.employeeId = employeeId;
}

@ManyToMany(cascade=CascadeType.ALL)
@JoinTable(
joinColumns={@JoinColumn(name="employeeId")},
inverseJoinColumns={@JoinColumn(name="projectId")}
)
private List<Project> projects;

@OneToOne(cascade=CascadeType.ALL)
@JoinColumn(name="AddressId")
private Address address;

public Address getAddress() {
return address;
}

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

public Set<String> getNickName() {
return nickName;
}

public void setNickName(Set<String> nickName) {
this.nickName = nickName;
}

public String getEmployeeName() {
return employeeName;
}

public void setEmployeeName(String employeeName) {
this.employeeName = employeeName;
}

public List<Project> getProjects() {
return projects;
}

public void setProjects(List<Project> projects) {
this.projects = projects;
}

public List getPhones() {
return phones;
}

public void setPhones(List phones) {
this.phones = phones;
}

}

package com.demo.beans;

import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.ManyToMany;

@Entity(name="Project")
@Inheritance(strategy=InheritanceType.JOINED) ----关联类型
@DiscriminatorColumn(name="ProjectType")
@DiscriminatorValue(value="Proj")
public class Project {
@Id
private int projectId;

private String projectName;

@ManyToMany(mappedBy="projects",cascade=CascadeType.ALL)
private List<Employee> employees;

public int getProjectId() {
return projectId;
}

public void setProjectId(int projectId) {
this.projectId = projectId;
}

public String getProjectName() {
return projectName;
}

public void setProjectName(String projectName) {
this.projectName = projectName;
}

public List<Employee> getEmployees() {
return employees;
}

public void setEmployees(List<Employee> employees) {
this.employees = employees;
}
}

package com.demo.beans;

import java.math.BigDecimal;

import javax.persistence.DiscriminatorValue;
import javax.persistence.Entity;

@Entity
@DiscriminatorValue(value="GlobProj")
public class GlobalProject extends Project {
private String projectCountry;
private BigDecimal projectBudget;
public String getProjectCountry() {
return projectCountry;
}
public void setProjectCountry(String projectCountry) {
this.projectCountry = projectCountry;
}
public BigDecimal getProjectBudget() {
return projectBudget;
}
public void setProjectBudget(BigDecimal projectBudget) {
this.projectBudget = projectBudget;
}
}

测试

Project project = new Project();
project.setProjectId(1);
project.setProjectName("Project");

// Create a Global Project
GlobalProject globalProject = new GlobalProject();
globalProject.setProjectId(2);
globalProject.setProjectName("Global Project");
globalProject.setProjectCountry("Brazil");
globalProject.setProjectBudget(new BigDecimal(150000));

// Create a Local Project
LocalProject localProject = new LocalProject();
localProject.setProjectId(3);
localProject.setProjectName("Local Project");
localProject.setProjectBudget(new BigDecimal(50000));

// Create a list of projects
List<Project> projects = new ArrayList<Project>();

// add the project into the list
projects.add(project);
projects.add(globalProject);
projects.add(localProject);

Employee employee = new Employee();


employee.setEmployeeName("Test Bai");
// Set the project into employee
employee.setProjects(projects);
userRepository.addEmployee(employee);

保存后的数据库中的表记录如下：

mysql> select * from employee_project;
+------------+-----------+
| employeeId | projectId |
+------------+-----------+
| 0 | 1 |
| 0 | 2 |
| 0 | 3 |
+------------+-----------+
3 rows in set (0.00 sec)