Hibernate Bidirectional Mapping short note

Here is my Hibernate/JPA bidirectional mapping short note.

One To One

Student	StudentRegistration
@Id @Column(name="student_id") private Long studentId;	@Id @Column(name="registration_no") private Long registrationNo;
@Column(name="student_name") private String name;	@Column(name="level") private String level;
	@Column(name="registration_date") @Temporal(TemporalType.DATE) private Date regDate;
@OneToOne StudentRegistration studentRegistration;	@OneToOne(mappedBy="studentRegistration") Student student;

Student is the owner, We add owner side property name to 'mappedBy'  of other side.

Database tables created by Hibernate

student

student_id	student_name	STUDENTRGISTRATION_registration_no

student_registration

registration_no	level	registration_date

If you want to change STUDENTRGISTRATION_registration_no column name to stu_reg_no add @JoinColumn annotation.

@OneToOne
@JoinColumn(name="stu_reg_no")
StudentRegistration studentRegistration;

  View Sample Code

Student.java

package com.sameera.entity;

import java.io.Serializable;
import javax.persistence.*;

@Entity
@Table(name = "student")
public class Student implements Serializable {

    @Id
    @Column(name = "student_id")
    private Integer studentId;

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

    @OneToOne
    //@JoinColumn(name="stu_reg_no")
    private StudentRegistration studentRegistration;


    public String getName() {
        return name;
    }

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

    public Integer getStudentId() {
        return studentId;
    }

    public void setStudentId(Integer studentId) {
        this.studentId = studentId;
    }

    public StudentRegistration getStudentRegistration() {
        return studentRegistration;
    }

    public void setStudentRegistration(StudentRegistration studentRegistration) {
        this.studentRegistration = studentRegistration;
    }
}

StudentRegistration.java

package com.sameera.entity;

import java.io.Serializable;
import java.util.Date;
import javax.persistence.*;


@Entity
@Table(name="student_registration")
public class StudentRegistration implements Serializable {

    @Id
    @Column(name = "registration_no")
    private Integer registrationNo;

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

    @Column(name = "registration_date")
    @Temporal(TemporalType.DATE)
    private Date registrationDate;
    
    @OneToOne(mappedBy="studentRegistration")
    private Student student;

    public String getLevel() {
        return level;
    }

    public void setLevel(String level) {
        this.level = level;
    }

    public Date getRegistrationDate() {
        return registrationDate;
    }

    public void setRegistrationDate(Date registrationDate) {
        this.registrationDate = registrationDate;
    }

    public Integer getRegistrationNo() {
        return registrationNo;
    }

    public void setRegistrationNo(Integer registrationNo) {
        this.registrationNo = registrationNo;
    }

    public Student getStudent() {
        return student;
    }

    public void setStudent(Student student) {
        this.student = student;
    }


}

One to Many/ Many to One 

Employee	Department
@Id @Column(name="emp_id") private Long id;	@Id @Column(name="dep_id") private Long id;
@Column(name="emp_name") private String name;	@Column(name="dep_name") private String name;
@ManyToOne Department department;	@OneToMany(mappedBy="department") List<Employee> emps;

Database tables created by Hibernate

employee

emp_id	emp_name	DEPARTMENT_dep_id

department

dep_id	dep_name

  View Sample Code

Employee.java

package com.sameera.entity;

import java.io.Serializable;
import javax.persistence.*;

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

    @Id
    @Column(name = "emp_id")
    private Long id;

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

    @ManyToOne
    private Department department;

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    public String getName() {
        return name;
    }

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

    public Long getId() {
        return id;
    }

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

    
}

Department.java

package com.sameera.entity;

import java.io.Serializable;
import java.util.List;
import javax.persistence.*;

@Entity
@Table(name="department")
public class Department implements Serializable {

    @Id
    @Column(name = "dep_id")
    private Long id;

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

    @OneToMany(mappedBy = "department")
    List<Employee> emps;

    public List<Employee> getEmps() {
        return emps;
    }

    public void setEmps(List<Employee> emps) {
        this.emps = emps;
    }

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

}

Many to Many

Employee	Project
@Id @Column(name="emp_id") private Long id;	@Id @Column(name="project_id") private Long id;
@Column(name="emp_name") private String name;	@Column(name="project_name") private String name;
@ManyToMany(mappedBy="employees") List<Project> projects;	@ManyToMany List<Employee> employees;

Database tables created by Hibernate

employee

emp_id	emp_name

project

project_id	project_name

project_employee

projects_project_id	employees_emp_id

If you want to change project_employee table name to pro_emp add @JoinTable annotaion
    @ManyToMany
    @JoinTable(name="pro_emp")
    List<Employee> employees;

  View Sample Code

Employee.java

package com.sameera.entity;

import java.io.Serializable;
import java.util.List;
import javax.persistence.*;

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

    @Id
    @Column(name = "emp_id")
    private Long id;

    @Column(name = "emp_name")
    private String name;
    
    @ManyToMany(mappedBy = "employees")
    private List<Project> projects;

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

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

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

Project.java

package com.sameera.entity;

import java.io.Serializable;
import java.util.List;
import javax.persistence.*;

@Entity
@Table(name = "project")
public class Project implements Serializable {

    @Id
    @Column(name = "project_id")
    private Long id;

    @Column(name = "project_name")
    private String name;
    
    @ManyToMany
    List<Employee> employees;

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

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

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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