Hibernate Relational Mapping

Hibernate Relational Mapping Well the main purpose of hibernate is to integrate into number of databases seamlessly. So in some cases where a bit hectic entity called “Foreign Key/Relation”  comes within a question arises how to tell hibernate of that. Hibernate gives us four main ways of expressing the relationship of one table with other, they are one-toone, one-to-many and many-to-one and many-to-many. So how we map the relation to other table… One-to-one: Exactly a unique row of a master table is to be associated with a unique row of child table or vice versa. One-to-many: Exactly a unique row of a table is to be associated with more than one rows of associate table. Many-to-one: Many rows of a table are associated with exactly one row of associate associate table (Inverse of One-to-many). One-to-many). Many-to-many: One (entire/partial) table is associated with other and vice versa. Well let us take a very simple example of t wo relational based tables with one-to one mapping where a row of an associate table will be dependent on primary key of a master table… Table: Person Field Person_id Fullname

Type String (Primary Key) String

Table: Employee Field Person_id Designation

Type String (Primary Key) String

In our case lets consider Person_id of Employee of  Employee table be “foreign key” that refers to Person_id of Person of Person table. The POJO classes of these tables in normal be as following… File Name: Person.java Package com.pojo; import java.io.Serializable; java.io.Serializable; public class Person implements Serializable { private String person_id; private String fullname;  //Getter and setter method method of Employee persistence persistence object (Employee.java)

private Employee employee; public Employee getEmployee() { return employee; } public void setEmployee(Employee employee) { this.employee=employee; } public String getPerson_id() { return this.person_id; } public String getFullname() { return this.fullname; } public void setPerson_id(String person_id) { this.person=person; } public void setFullname(String fullname) { this.fullname=fullname; } } File Name: Employee.java Package com.pojo; import java.io.Serializable; public class Employee implements Serializable { private String person_id; private String designation;  //Getter and setter method of Person persistence object (Person.java) private Person person; public Person getPerson() { return this.person;

} Public void setPerson(Person person) { this.person=person; } public String getPerson_id() { return this.person_id; } public String getDesignation() { return this.designation; } public void setPerson_id(String person_id) { this.person=person; } public void setDesignation(String designation) { this. designation = designation; } } The hibernate xml files will be… File Name: person.hbm.xml

File Name: employee.hbm.xml In your action servlet or DAO … For saving import com.pojo.Person; import com.pojo.Employee; …………………………….. …………………………………… String id=”abc”; String name=”XYZ”  String design=”Programmer”;  //Create persistence objects Person personPersistance=new Person(); Employee employeePersistance=new Employee(); employeePersistance.setPerson_id(id); employeePersistance.setDesignation(desig); personPersistance.setPerson_id(id); personPersistance.setFullname(name); personPersistance.setEmployee(employee); personPersistance.save(person);

 //Similarly for update personPersistance.update(person); …………………………….. ……………………………………

For deleting …………………………….. ……………………………………  //Create persistence objects Person personPersistance=new Person(); Employee employeePersistance=new Employee(); employeePersistance.setPerson_id(id); employeePersistance.setDesignation(desig); personPersistance.setPerson_id(id); personPersistance.setFullname(name); personPersistance.delete(person);  //No need to set employeePersistance for personPersistance. …………………………….. ……………………………………