Java Tutorial/JPA/One To Many Mapping

One To Many Bidirectional

File: Department.java

import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    private Collection<Student> students;
    
    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 Collection<Student> getStudents() {
      return students;
    }
    public void setStudent(Collection<Student> students) {
      this.students = students;
    }
    public String toString() {
        return "Department id: " + getId() + 
               ", name: " + getName();
    }
}

One To Many Cascade.All

File: Student.java

import javax.persistence.CascadeType;
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(cascade=CascadeType.ALL)
  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";
  }
}

One To Many Join Table Setup

File: Phone.java

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
@Entity
public class Phone {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    @Column(name="NUM")
    private String number;
    private String type;
    
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    
    public String getNumber() {
        return number;
    }
    
    public void setNumber(String phoneNo) {
        this.number = phoneNo;
    }
    
    public String getType() {
        return type;
    }
    
    public void setType(String phoneType) {
        this.type = phoneType;
    }
    public String toString() {
        return "Phone id: " + getId() + 
               ", no: " + getNumber() +
               ", type: " + getType();
    }
}

One To Many List Collection

File: Student.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 "Student id: " + getId() + " name: " + getName() + 
               " with " + getDepartment();
    }
}

One To Many Map Collection

File: Department.java

import java.util.HashMap;
import java.util.Map;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;
@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    @MapKey(name="name")
    private Map<String, Student> students;
    public Department() {
        students = new HashMap<String, Student>();
    }
    
    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 void addStudent(Student student) {
        if (!getStudents().containsKey(student.getName())) {
            getStudents().put(student.getName(), student);
            if (student.getDepartment() != null) {
                student.getDepartment().getStudents().remove(student.getName());
            }
            student.setDepartment(this);
        }
    }
    
    public Map<String,Student> getStudents() {
        return students;
    }
    public String toString() {
        return "Department id: " + getId() + 
               ", name: " + getName();
    }
}

One To Many With Mapped By To remove Mapping Table

File: Department.java

import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;
    @OneToMany(mappedBy="department",cascade=CascadeType.ALL)
    private Set<Student> students;
    
    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 Set<Student> getStudents() {
      return students;
    }
    public void setStudent(Set<Student> students) {
      this.students = students;
    }
    public String toString() {
        return "Department id: " + getId() + 
               ", name: " + getName()+"Student:"+ students;
    }
}

One To Many With Order By Setting

File: Department.java

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.OrderBy;
@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    @OrderBy("name ASC")
    private List<Student> students;
    public Department() {
        students = new ArrayList<Student>();
    }
    
    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 void addStudent(Student student) {
        if (!getStudents().contains(student)) {
            getStudents().add(student);
            if (student.getDepartment() != null) {
                student.getDepartment().getStudents().remove(student);
            }
            student.setDepartment(this);
        }
    }
    
    public Collection<Student> getStudents() {
        return students;
    }
    public String toString() {
        return "Department id: " + getId() + 
               ", name: " + getName();
    }
}

Set target Entity For One To Many Mapping

File: Student.java

import javax.persistence.CascadeType;
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 ;
  }
}

Use Collection In One To Many Mapping

File: Department.java

import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    private Collection<Student> students;
    
    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 Collection<Student> getStudents() {
      return students;
    }
    public void setStudent(Collection<Student> students) {
      this.students = students;
    }
    public String toString() {
        return "Department id: " + getId() + 
               ", name: " + getName();
    }
}