Many-to-One relationship in real world:
Two items are said to be in Many-to-One relationship if one item is belong to the many occurrences of other item. E.g. Many employees – one department.
Many-to-One relationship in programming:
Two entities are said to be in Many-to-One relationship if one entity belongs to many occurrence of other entity. Note: One-to-Many and Many-to-One are both same it depends upon the side of entities in the relationship. As one department – many employees refers to the One-to-Many and Many employees – one department refers to the Many-to-One.
Example:
Student.java
/** * This class represents a persistent class for Student. * @author w3spoint */ public class Student { //data members private int studentId; private String firstName; private String lastName; private String rollNo; private int age; private StudentClass studentClass; //no-argument constructor public Student(){ } //argument constructor public Student(String firstName, String lastName, String rollNo, int age, StudentClass studentClass){ this.firstName = firstName; this.lastName = lastName; this.rollNo = rollNo; this.age = age; this.studentClass = studentClass; } //getter and setter methods public int getStudentId() { return studentId; } public void setStudentId(int studentId) { this.studentId = studentId; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getRollNo() { return rollNo; } public void setRollNo(String rollNo) { this.rollNo = rollNo; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public StudentClass getStudentClass() { return studentClass; } public void setStudentClass(StudentClass studentClass) { this.studentClass = studentClass; } } |
StudentClass.java
/** * This class represents a persistent class for Subject. * @author w3spoint */ public class StudentClass { //data members private String classId; private String className; //no argument constructor public StudentClass(){ } //argument constructor public StudentClass(String className){ this.className = className; } //getter and setter methods public String getClassId() { return classId; } public void setClassId(String classId) { this.classId = classId; } public String getClassName() { return className; } public void setClassName(String className) { this.className = className; } } |
hibernate.cfg.xml
<?xml version='1.0' encoding='UTF-8'?> <!DOCTYPE hibernate-configuration SYSTEM "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <session-factory> <property name="dialect"> org.hibernate.dialect.OracleDialect </property> <property name="connection.url"> jdbc:oracle:thin:@localhost:1521:XE </property> <property name="connection.username"> system </property> <property name="connection.password"> oracle </property> <property name="connection.driver_class"> oracle.jdbc.driver.OracleDriver </property> <property name="hbm2ddl.auto"> update </property> <property name="show_sql"> true </property> <mapping resource="student.hbm.xml"/> <mapping resource="studentclass.hbm.xml"/> </session-factory> </hibernate-configuration> |
student.hbm.xml
<?xml version='1.0' encoding='UTF-8'?> <!DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.w3spoint.business.Student" table="Student"> <id name="studentId" type="int" column="Student_Id"> <generator class="native"></generator> </id> <property name="firstName" column="First_Name" type="string"/> <property name="lastName" column="Last_Name" type="string"/> <property name="rollNo" column="RollNo" type="string"/> <property name="age" column="Age" type="int"/> <many-to-one name="studentClass" column="Student_Class" class="com.w3spoint.business.StudentClass" cascade="all"> </many-to-one> </class> </hibernate-mapping> |
studentclass.hbm.xml
<?xml version='1.0' encoding='UTF-8'?> <!DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.w3spoint.business.StudentClass" table="StuClass"> <id name="classId" column="Class_Id" type="string"> <generator class="native"></generator> </id> <property name="className" column="Class_Name" type="string"></property> </class> </hibernate-mapping> |
HibernateUtil.java
import org.hibernate.SessionFactory; import org.hibernate.cfg.Configuration; /** * This is a utility class for getting the hibernate session object. * @author w3spoint */ public class HibernateUtil { private static final SessionFactory sessionFactory = buildSessionFactory(); private static SessionFactory buildSessionFactory() { SessionFactory sessionFactory = null; try { //Create the configuration object. Configuration configuration = new Configuration(); //Initialize the configuration object //with the configuration file data configuration.configure("hibernate.cfg.xml"); // Get the SessionFactory object from configuration. sessionFactory = configuration.buildSessionFactory(); } catch (Exception e) { e.printStackTrace(); } return sessionFactory; } public static SessionFactory getSessionFactory() { return sessionFactory; } } |
HibernateTest.java
import com.w3spoint.persistence.StudentDBOperations; /** * This class is used for the hibernate operations. * @author w3spoint */ public class HibernateTest { public static void main(String args[]){ StudentClass studentClass = new StudentClass("MCA1"); //Create the student object. Student student1 = new Student("Sandy", "Sethi", "MCA/07/19", 27, studentClass); Student student2 = new Student("Munish", "Mehta", "MCA/07/04", 27, studentClass); StudentDBOperations obj = new StudentDBOperations(); //insert student object. obj.addStudent(student1); obj.addStudent(student2); //show all student object. obj.showAllStudentDetails(); } } |
StudentDBOperations.java
import java.util.List; import org.hibernate.HibernateException; import org.hibernate.Session; import org.hibernate.Transaction; import com.w3spoint.business.Student; import com.w3spoint.business.StudentClass; /** * This class contains the methods to interact with database. * @author w3spoint */ public class StudentDBOperations { /** * This method is used to insert a new student record. * @param student * @return studentId * @author w3spoint */ public Integer addStudent(Student student){ Transaction tx = null; Integer studentId = null; //Get the session object. Session session = HibernateUtil.getSessionFactory().openSession(); try{ tx = session.beginTransaction(); studentId = (Integer) session.save(student); tx.commit(); }catch (HibernateException e) { if(tx!=null){ tx.rollback(); } e.printStackTrace(); }finally { session.close(); } return studentId; } /** * This method is used retrieve and show the records. * @author w3spoint */ public void showAllStudentDetails(){ Transaction tx = null; //Get the session object. Session session = HibernateUtil.getSessionFactory().openSession(); try{ tx = session.beginTransaction(); List<Student> students = session.createQuery("FROM Student").list(); for(Student student : students){ System.out.println("First Name: " + student.getFirstName()); System.out.println("Last Name: " + student.getLastName()); System.out.println("RollNo: " + student.getRollNo()); System.out.println("Age: " + student.getAge()); StudentClass studentClass = student.getStudentClass(); System.out.println("Class Name:" + studentClass.getClassName()); System.out.println("Class Id:" + studentClass.getClassId()); } tx.commit(); }catch (HibernateException e) { if(tx!=null){ tx.rollback(); } e.printStackTrace(); }finally { session.close(); } } } |
Output:
Hibernate: select hibernate_sequence.nextval from dual Hibernate: select hibernate_sequence.nextval from dual Hibernate: insert into StuClass (Class_Name, Class_Id) values (?, ?) Hibernate: insert into Student (First_Name, Last_Name, RollNo, Age, Student_Class, Student_Id) values (?, ?, ?, ?, ?, ?) Hibernate: select hibernate_sequence.nextval from dual Hibernate: insert into Student (First_Name, Last_Name, RollNo, Age, Student_Class, Student_Id) values (?, ?, ?, ?, ?, ?) Hibernate: update StuClass set Class_Name=? where Class_Id=? Hibernate: select student0_.Student_Id as Student1_0_, student0_.First_Name as First2_0_, student0_.Last_Name as Last3_0_, student0_.RollNo as RollNo0_, student0_.Age as Age0_, student0_.Student_Class as Student6_0_ from Student student0_ First Name: Sandy Last Name: Sethi RollNo: MCA/07/19 Age: 27 Hibernate: select studentcla0_.Class_Id as Class1_1_0_, studentcla0_.Class_Name as Class2_1_0_ from StuClass studentcla0_ where studentcla0_.Class_Id=? Class Name:MCA1 Class Id:240 First Name: Munish Last Name: Mehta RollNo: MCA/07/04 Age: 27 Class Name:MCA1 Class Id:240 |
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