Criteria and Projection Example in Hibernate

Criteria is used to get complete data from database and return complete object ,It is used to apply condition in object using Restriction class and Criterion Interface.
It is only for Data Selection  not for Data Insertion ,Updation and Deletion.
Code of  Data Selection :-
import java.util.Iterator;
import java.util.List;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Criterion;
import org.hibernate.criterion.Restrictions;
import scs.Student;
public class CriteriaExample {
public static void main(String[] args) {
Configuration cfg = new Configuration();
cfg.configure("hibernate.cfg.xml");
        SessionFactory sf = cfg.buildSessionFactory();
        Session s =sf.openSession();
        Criteria crt = s.createCriteria(Student.class);
       // Criterion crt1 = Restrictions.gt("fees", 12000);
        Criterion crt1 = Restrictions.like("sname", "%m%");
        crt.add(crt1);
        List lst = crt.list();
        Iterator it = lst.iterator();
        while(it.hasNext())
        {
        Student stu = (Student)it.next();
        System.out.println(stu.getRno() +" "+stu.getSname()+" "+stu.getBranch()+" "+stu.getFees());
        }
       
       s.close();
}
}

Projection:-

If we want to retrieve particular column data then we will use Projection Interface.  Hibernate uses projection to display particular data members of the class.

Criterial interface has setProjection() to implement Projection functionality.

Criterion ct = Certierta.createCriteria(ProjoClassname);

ct.setProjection(Projections.property("variablename"));

Now I am implementing Student Pojo Class that contains (rno, name, branch, and fees) data members. now I will display fees column data.

1)   Create Pojo Class:-

package scs;

public class Student {

private int rno;

private String sname;

private String branch;

private int fees;

public int getRno() {

return rno;

}

public void setRno(int rno) {

this.rno = rno;

}

public String getSname() {

return sname;

}

public void setSname(String sname) {

this.sname = sname;

}

public String getBranch() {

return branch;

}

public void setBranch(String branch) {

this.branch = branch;

}

public int getFees() {

return fees;

}

public void setFees(int fees) {

this.fees = fees;

}

}

2) Create hibernate.cfg.xml

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<property name="connection.driver_class">com.mysql.jdbc.Driver</property>

<property name="connection.url">jdbc:mysql://localhost:3306/java56db</property>

<property name="connection.username">root</property>

<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

<property name="hbm2ddl.auto">update</property>

<property name="show_sql">true</property>

 <mapping resource="student.hbm.xml"></mapping>

</session-factory>

</hibernate-configuration>
3)  create    student.hbm.xml

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<class name="scs.Student" table="tbl_Student">

<id name="rno" column="rno">

<generator class="assigned"></generator>

</id>

<property name="sname" />

<property name="branch"/>

<property name="fees" />

</class>

</hibernate-mapping>

4)  Create Code to implement Projection:-

        Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf= cfg.buildSessionFactory();

Session s = sf.openSession();

Criteria ct = s.createCriteria(Student.class);

        ct.setProjection(Projections.property("fees"));

        List lst = ct.list();

Iterator it = lst.iterator();

while(it.hasNext())

{

Object o = it.next();

        System.out.println(o);

}

s.close();

sf.close();

ProjectionList:-

It is used to retrieve multiple column data, we can select more than one column using Projectionlist Object.

Criteria ct = s.createCriteria(Student.class);

ProjectionList p1=Projections.projectionList();

 p1.add(Projections.property("rno"));

p1.add(Projections.property("fees"));

ct.setProjection(p1);

Now I am explaining the complete code of ProjectionSet for Student Pojo Class that will fetch the rno and fees column data.

public class ViewAllStudent {

public static void main(String args[])

{

Configuration cfg = new Configuration();

cfg.configure("hibernate.cfg.xml");

SessionFactory sf= cfg.buildSessionFactory();

Session s = sf.openSession();

Criteria ct = s.createCriteria(Student.class);

ProjectionList p1=Projections.projectionList();

p1.add(Projections.property("rno"));

p1.add(Projections.property("fees"));

    ct.setProjection(p1);

List lst = ct.list();

Iterator it = lst.iterator();

while(it.hasNext())

{

Object o[] =(Object[]) it.next();

System.out.println(o[0] + " "+o[1]);

}

s.close();

sf.close();

}

}