What is JPA Sub queries and how to use it you application?
What is JPA Sub queries and how to use it you application?In this section, you will see how to use sub-queries in your JPA application. Sub-queries allows you for querying the vast number of data components in a single query.
JPA Sub-queries:
Query query=em.createQuery ("SELECT st FROM Student st WHERE st.sroll= (SELECT st.sroll FROM Student st WHERE st.sroll>100 AND st.sroll<102)"); |
For JPA Grouping application, you need the following artifacts:
Database Table: student
CREATE TABLE `student` ( `id` int(11) NOT NULL auto_increment, `sname` varchar(100) NOT NULL, `sroll` int(11) NOT NULL, `scourse` varchar(10) NOT NULL, PRIMARY KEY (`id`) ) |
Model Class: Student.java
/** * */ package roseindia; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.NamedQueries; import javax.persistence.NamedQuery; import javax.persistence.Table; /** * @author Administrator * */ @Entity @Table(name="student") public class Student { @Id @GeneratedValue private int id; /** * @return the id */ public int getId() { return id; } /** * @param id the id to set */ public void setId(int id) { this.id = id; } @Column(name="sname", length=100,nullable=false) private String sname; /** * @return the sname */ public String getSname() { return sname; } /** * @param sname the sname to set */ public void setSname(String sname) { this.sname = sname; } @Column(name="sroll",nullable=false) private int sroll; /** * @return the sroll */ public int getSroll() { return sroll; } /** * @param sroll the sroll to set */ public void setSroll(int sroll) { this.sroll = sroll; } @Column(name="scourse",length=10,nullable=false) private String scourse; /** * @return the scourse */ public String getScourse() { return scourse; } /** * @param scourse the scourse to set */ public void setScourse(String scourse) { this.scourse = scourse; } } |
Main Class: JPASubQueries.java
/** * */ package roseindia; import java.util.Iterator; import java.util.List; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.EntityTransaction; import javax.persistence.Persistence; import javax.persistence.Query; /** * @author Administrator * */ public class JPASubQueries { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub EntityManagerFactory emf=Persistence.createEntityManagerFactory("jpa"); EntityManager em=emf.createEntityManager(); try{ EntityTransaction entr=em.getTransaction(); entr.begin(); Query query=em.createQuery("SELECT st FROM Student st WHERE st.sroll=(SELECT st.sroll FROM Student st WHERE st.sroll>100 AND st.sroll<102)"); List stList=query.getResultList(); Iterator stIterator=stList.iterator(); while(stIterator.hasNext()){ Student st=(Student)stIterator.next(); System.out.print("id:"+st.getId()); System.out.print(" sname:"+st.getSname()); System.out.print(" sroll:"+st.getSroll()); System.out.print(" scourse:"+st.getScourse()); System.out.println(); } entr.commit(); } finally{ em.close(); } } }
Output:
log4j:WARN No appenders could be
found for logger log4j:WARN Please initialize the log4j system properly. Hibernate: select student0_.id as id0_, student0_.scourse
as id:1 sname:Vinod sroll:101 scourse:MCA |
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