Java Tutorial/JPA/Many to One Mapping

Many To One Cascade Merge

File: Department.java

   <source lang="java">

import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; @Entity public class Department {

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   public int getId() {
       return id;
   }
   
   public void setId(int id) {
       this.id = id;
   }
   
   public String getName() {
       return name;
   }
   
   public void setName(String deptName) {
       this.name = deptName;
   }
   public String toString() {
       return "Department id: " + getId() + 
              ", name: " + getName();
   }

}</source>

Many To One Cascade Remove

File: Student.java

   <source lang="java">

import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.ManyToOne; @Entity public class Student {

   @Id
   private int id;
   private String name;
   
   @ManyToOne(cascade=CascadeType.REMOVE)
   Address address;
   public int getId() {
       return id;
   }
   
   public void setId(int id) {
       this.id = id;
   }
   
   public String getName() {
       return name;
   }
   
   public void setName(String name) {
       this.name = name;
   }
   public Address getAddress() {
       return address;
   }
   
   public void setAddress(Address address) {
       this.address = address; 
   }
   public String toString() {
       return "Student id: " + getId() + " name: " + getName() +
              " with " + getAddress();
   }

}</source>

Many To One Cascasde Persist

File: Student.java

   <source lang="java">

import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.ManyToOne; @Entity public class Student {

   @Id
   private int id;
   private String name;
   
   @ManyToOne(cascade=CascadeType.PERSIST)
   Address address;
   public int getId() {
       return id;
   }
   
   public void setId(int id) {
       this.id = id;
   }
   
   public String getName() {
       return name;
   }
   
   public void setName(String name) {
       this.name = name;
   }
   public Address getAddress() {
       return address;
   }
   
   public void setAddress(Address address) {
       this.address = address; 
   }
   public String toString() {
       return "Student id: " + getId() + " name: " + getName() +
              " with " + getAddress();
   }

}</source>

Many To One Insertable Nullable Updatable

File: Department.java

   <source lang="java">

import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; @Entity public class Department {

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   public int getId() {
       return id;
   }
   
   public void setId(int id) {
       this.id = id;
   }
   
   public String getName() {
       return name;
   }
   
   public void setName(String deptName) {
       this.name = deptName;
   }
   public String toString() {
       return "Department id: " + getId() + 
              ", name: " + getName();
   }

}</source>

Many To One Mapping Manually Linking

File: Student.java

   <source lang="java">

import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.ManyToOne; @Entity public class Student {

 @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
 private int id;
 private String name;
 @ManyToOne
 private Department department;
 public int getId() {
   return id;
 }
 public void setId(int id) {
   this.id = id;
 }
 public String getName() {
   return name;
 }
 public void setName(String name) {
   this.name = name;
 }

 public Department getDepartment() {
   return department;
 }
 public void setDepartment(Department department) {
   this.department = department;
 }
 public String toString() {
   return "\n\nID:" + id + "\nName:" + name + "\n\n";
 }

}</source>

Many To One Mapping Unique Join Column

File: Student.java

   <source lang="java">

import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; @Entity public class Student {

 @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
 private int id;
 private String name;
 @ManyToOne(cascade=CascadeType.ALL)
 @JoinColumn(name="DEPT_ID", unique= true, nullable=true, insertable=true, updatable=true)
 private Department department;
 public int getId() {
   return id;
 }
 public void setId(int id) {
   this.id = id;
 }
 public String getName() {
   return name;
 }
 public void setName(String name) {
   this.name = name;
 }

 public Department getDepartment() {
   return department;
 }
 public void setDepartment(Department department) {
   this.department = department;
 }
 public String toString() {
   return "\n\nID:" + id + "\nName:" + name + "\n\n" + department;
 }

}</source>

Many to One Map With Entity Hierarchy

File: Employee.java

   <source lang="java">

import java.util.Date; import javax.persistence.AssociationOverride; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Inheritance; import javax.persistence.InheritanceType; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; import javax.persistence.MappedSuperclass; import javax.persistence.Table; import javax.persistence.Temporal; import javax.persistence.TemporalType; @Entity @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) public abstract class Employee {

 @Id
 private int id;
 private String name;
 @Temporal(TemporalType.DATE)
 private Date startDate;
 public int getId() {
   return id;
 }
 public void setId(int id) {
   this.id = id;
 }
 public String getName() {
   return name;
 }
 public void setName(String name) {
   this.name = name;
 }
 public Date getStartDate() {
   return startDate;
 }
 public void setStartDate(Date startDate) {
   this.startDate = startDate;
 }
 public String toString() {
   return "Employee id: " + getId() + " name: " + getName();
 }

} @MappedSuperclass abstract class CompanyEmployee extends Employee {

 private int vacation;
 @ManyToOne
 private Employee manager;
 public int getVacation() {
   return vacation;
 }
 public void setVacation(int vacation) {
   this.vacation = vacation;
 }
 public Employee getManager() {
   return manager;
 }
 public void setManager(Employee manager) {
   this.manager = manager;
 }

} @Entity @AssociationOverride(name = "manager", joinColumns = @JoinColumn(name = "MGR")) class PartTimeEmployee extends CompanyEmployee {

 private float hourlyRate;
 public float getHourlyRate() {
   return hourlyRate;
 }
 public void setHourlyRate(float hourlyRate) {
   this.hourlyRate = hourlyRate;
 }
 public String toString() {
   return "PartTimeEmployee id: " + getId() + " name: " + getName();
 }

} @Entity class FullTimeEmployee extends CompanyEmployee {

 private long salary;

 private long pensionContribution;
 public long getPensionContribution() {
   return pensionContribution;
 }
 public void setPensionContribution(long pension) {
   this.pensionContribution = pension;
 }
 public long getSalary() {
   return salary;
 }
 public void setSalary(long salary) {
   this.salary = salary;
 }
 public String toString() {
   return "FullTimeEmployee id: " + getId() + " name: " + getName();
 }

}</source>

Many To One Set Join Column Name

File: Student.java

   <source lang="java">

import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; @Entity public class Student {

 @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
 private int id;
 private String name;
 @ManyToOne(cascade=CascadeType.ALL)
 @JoinColumn(name="DEPT_ID")
 private Department department;
 public int getId() {
   return id;
 }
 public void setId(int id) {
   this.id = id;
 }
 public String getName() {
   return name;
 }
 public void setName(String name) {
   this.name = name;
 }

 public Department getDepartment() {
   return department;
 }
 public void setDepartment(Department department) {
   this.department = department;
 }
 public String toString() {
   return "\n\nID:" + id + "\nName:" + name + "\n\n" + department;
 }

}</source>

Mapping Relationship State

File: Project.java

   <source lang="java">

import java.util.ArrayList; import java.util.Collection; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.OneToMany; @Entity public class Project {

   @Id private int id;
   private String name;
   
   @OneToMany(mappedBy="project")
   private Collection<ProjectAssignment> assignments;
   public Project() {
       assignments = new ArrayList<ProjectAssignment>();
   }
   
   public int getId() {
       return id;
   }
   
   public void setId(int projectNo) {
       this.id = projectNo;
   }
   
   public String getName() {
       return name;
   }
   
   public void setName(String projectName) {
       this.name = projectName;
   }
   
   public Collection<ProjectAssignment> getAssignments() {
       return assignments;
   }
   
   public String toString() {
       return " no: " + getId() + 
               ", name: " + getName();
   }

}</source>