Hibernate Mapping

1. OneToOne
2. OneToMany
3. ManyToOne
4. ManyToOne

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

   @Id  
   @Column(name="student_id")  
   @GeneratedValue(strategy= GenerationType.AUTO)  
   private String studentId;  

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

   @Column(name="date_of_birth")  
   private String dob;  

   @OneToOne  
   @JoinColumn(name="student_id")  
   private Address address;  

   @ManyToOne  
   @JoinColumn(name="course_id")  
   private StudentCourse studentCourse;  

   @OneToMany(mappedBy = "monthAttendancePK.studentId")  
   private Set<MonthAttendance> monthAttendances;  

   @ManyToMany  
   @JoinTable(name = "student_subject",joinColumns = @JoinColumn(name = "student_id"),  
       inverseJoinColumns = @JoinColumn(name = "subject_id"))  
   private Set<Subject> subjects;  

   /*  
   *Other properties and mutators  
   */  
 }  

Address.java

 @Entity  
 @Table(name="student_address")  
 public class Address {  
   @Id  
   @Column(name="student_id")  
   private String studentId;  

   private String location;  

   private String city;  

   private String country;  

   /*   
   *Other properties and mutators   
   */   
 }  

Notice the variables location, city, country. We didn’t specify the column annotation. Because the variable name and database column name both are same here. So no need to specify it explicitly.

StudentCourse.java

 @Entity  
 @Table(name="course_details")  
 public class StudentCourse implements Serializable {  

   @Id  
   @Column(name="course_id")  
   @GeneratedValue(strategy= GenerationType.IDENTITY)  
   private String courseId;  

   @Column(name="course_name")  
   private String courseName;  

   private String department;  

   @Column(name="class_location")  
   private String classLocation;  

   private String hod;  

   /*   
   *Other properties and mutators   
   */   
 }  

Composite Primary Key:
Creating a entity class for the month_attendance table is quite different from all other entities which we saw above. Because month_attendance has composite primary key means it’s a combination of  two different columns, student_id and month_year. So we declare MonthAttendancePK entity, which holds only the primary key columns, along with MonthAttendance entity which holds all column properties other than the primary keys. We will get a better understanding, when we look at the below code.

MonthAttendancePK.java

 @Embeddable  
 public class MonthAttendancePK implements Serializable {  

   @Column(name="student_id")  
   private String studentId;  

   @Column(name="month_year")  
   private String monthYear;  

   /*   
   *Other properties and mutators   
   */   
 }  

The below MonthAttendance class will have this MonthAttendancePK and it’s annotated by @EmbeddedId

MonthAttendance.java

 @Entity  
 @Table(name="month_attendance")  
 public class MonthAttendance implements Serializable {  

   @EmbeddedId  
   private MonthAttendancePK monthAttendancePK;  

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

   @Column(name="medical_leaves")  
   private String medicalLeaves;  

   @Column(name="planned_leaves")  
   private String plannedLeaves;  

   @Column(name="urgent_leaves")  
   private String urgentLeaves;  

   /*   
   *Other properties and mutators   
   */   

 }  

Please take a note that we didn’t use the @Id annotation, when it comes to composite primary key. Let’s have a look at the many to many relationship.

Subject.java

 @Entity  
 @Table(name="academic_subject")  
 public class Subject {  

   @Id  
   @Column(name="subject_id")  
   @GeneratedValue(strategy= GenerationType.AUTO)  
   private String subjectId;  

   @Column(name="subject_name")  
   private String subjectName;  

   @Column(name="recommended_books")  
   private String recommendedBooks;  

   /*   
   *Other properties and mutators   
   */   
 }  

We didn’t have any entity for the table student_subject. Because it’s just a mapping table represents the many to many relationship between student and academic_subject.

SessionFactory:

   <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">  
     <property name="driverClassName" value="com.mysql.jdbc.Driver" />  
     <property name="url" value="jdbc:mysql://localhost:3306/usersproduct" />  
     <property name="username" value="root"/>  
     <property name="password" value="9may89mysql"/>  
   </bean>  
   <!-- Hibernate 4 SessionFactory Bean definition -->  
   <bean id="sessionFactory"  
      class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">  
     <property name="dataSource" ref="dataSource" />  
     <property name="annotatedClasses">  
       <list>  
         <value>com.sample.model.Student</value>  
         <value>com.sample.model.StudentCourse</value>  
         <value>com.sample.model.MonthAttendance</value>  
         <value>com.sample.model.Subject</value>  
         <value>com.sample.model.Address</value>  
       </list>  
     </property>  
     <property name="hibernateProperties">  
       <props>  
         <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>  
         <prop key="hibernate.show_sql">true</prop>  
       </props>  
     </property>  
   </bean>  
   <tx:annotation-driven transaction-manager="transactionManager"/>  
   <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">  
     <property name="sessionFactory" ref="sessionFactory" />  
   </bean>  

 @Repository  
 public class StudentDaoImpl implements StudentDao{  
   @Autowired(required = true)  
   private SessionFactory sessionFactory;  
   public List<Student> listStudents() {  
     Session session = this.sessionFactory.openSession();  
     List<Student> studentList = session.createQuery("from Student").list();  
     return studentList;  
   }  
   public Student getStudentData(String studentId) {  
     Session session = this.sessionFactory.openSession();  
     List<Student> studentList = new ArrayList<Student>();  
     Student student = session.get(Student.class,studentId);  
     return student;  
   }  
 }