Hibernate one to many relationship query

[arjun narahari]

Hii this is arjun narahari 

i have been watching ur tutorials on a frequent basis , i started up with hibernate recently

actually i m kinda stuck in between one to many relationship , it would be a grt help from u Koushik sir if u just guide me as in where i m making the mistake

this is my College class

package com.hibernate.arjun3;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

@Entity

public class College {

private String name;

@Id

@GeneratedValue

private int college_id;

private String location;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public int getCollege_id() {

return college_id;

}

public void setCollege_id(int college_id) {

this.college_id = college_id;

}

public String getLocation() {

return location;

}

public void setLocation(String location) {

this.location = location;

}

}

this is my students class

package com.hibernate.arjun3;

import java.util.ArrayList;

import java.util.Collection;

import javax.persistence.CascadeType;

import javax.persistence.ElementCollection;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinTable;

import javax.persistence.OneToMany;

import javax.persistence.JoinColumn;

@Entity

public class Students {

private String firstname;

private String lastname;

@Id

@GeneratedValue

private int college_id;

@ElementCollection

@OneToMany(cascade = CascadeType.ALL)

@JoinTable(name="College_Students" , joinColumns=@JoinColumn(name="College_Id"))

private Collection<College> college = new ArrayList<College>();

public Collection<College> getCollege() {

return college;

}

public void setCollege(Collection<College> college) {

this.college = college;

}

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 int getCollege_id() {

return college_id;

}

public void setCollege_id(int college_id) {

this.college_id = college_id;

}

}

my Main class

package com.hibernate.arjun3;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.AnnotationConfiguration;

public class Main1 {

public static void main(String args[]) {

College colg = new College();

colg.setName("Vivekanand");

colg.setLocation("Chembur");

Students students = new Students();

students.setFirstname("Arjun");

students.setLastname("Narahari");

Students students2 = new Students();

students2.setFirstname("Sagar");

students2.setLastname("Abhyankar");

students.getCollege().add(colg);

students2.getCollege().add(colg);

SessionFactory factory = new AnnotationConfiguration().configure().buildSessionFactory();

Session session = factory.openSession();

session.beginTransaction();

session.save(students);

session.save(students2);

session.getTransaction().commit();

                session.close();

factory.close();

}

}

This is the error i m getting after executing the main class

INFO: HHH000227: Running hbm2ddl schema export

Hibernate: alter table Students_College drop foreign key FK_qk8e1fl454umkjvarmovmdgrp

Hibernate: alter table Students_College drop foreign key FK_n2cycly15ecddgky71345r3u

Hibernate: drop table if exists College

Hibernate: drop table if exists Students

Hibernate: drop table if exists Students_College

Hibernate: create table College (college_id integer not null auto_increment, location varchar(255), name varchar(255), primary key (college_id))

Hibernate: create table Students (college_id integer not null auto_increment, firstname varchar(255), lastname varchar(255), primary key (college_id))

Hibernate: create table Students_College (Students_college_id integer not null, college_college_id integer not null)

Hibernate: alter table Students_College add constraint UK_qk8e1fl454umkjvarmovmdgrp  unique (college_college_id)

Hibernate: alter table Students_College add constraint FK_qk8e1fl454umkjvarmovmdgrp foreign key (college_college_id) references College (college_id)

Hibernate: alter table Students_College add constraint FK_n2cycly15ecddgky71345r3u foreign key (Students_college_id) references Students (college_id)

Sep 27, 2014 12:21:01 PM org.hibernate.tool.hbm2ddl.SchemaExport execute

INFO: HHH000230: Schema export complete

Hibernate: insert into Students (firstname, lastname) values (?, ?)

Hibernate: insert into College (location, name) values (?, ?)

Hibernate: insert into Students (firstname, lastname) values (?, ?)

Hibernate: insert into Students_College (Students_college_id, college_college_id) values (?, ?)

Hibernate: insert into Students_College (Students_college_id, college_college_id) values (?, ?)

Sep 27, 2014 12:21:01 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions

WARN: SQL Error: 1062, SQLState: 23000

Sep 27, 2014 12:21:01 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions

ERROR: Duplicate entry '1' for key 'UK_qk8e1fl454umkjvarmovmdgrp'

Sep 27, 2014 12:21:01 PM org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl release

INFO: HHH000010: On release of batch it still contained JDBC statements

Exception in thread "main" org.hibernate.exception.ConstraintViolationException: could not execute statement

at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:72)

at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)

at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:126)

at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:112)

at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:211)

at org.hibernate.engine.jdbc.batch.internal.NonBatchingBatch.addToBatch(NonBatchingBatch.java:62)

at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1311)

at org.hibernate.action.internal.CollectionRecreateAction.execute(CollectionRecreateAction.java:67)

at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:463)

at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:349)

at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:350)

at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:56)

at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1222)

at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:425)

at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)

at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:177)

at com.hibernate.arjun3.Main1.main(Main1.java:31)

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '1' for key 'UK_qk8e1fl454umkjvarmovmdgrp'

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)

at java.lang.reflect.Constructor.newInstance(Unknown Source)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:408)

at com.mysql.jdbc.Util.getInstance(Util.java:383)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1049)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4208)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4140)

at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2597)

at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2758)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2826)

at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2082)

at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2334)

at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2262)

at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2246)

at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:208)

... 12 more

expecting ur reply asap

thanking you

Regards 

Arjun Narahari

[Rama krishna]

Dear narahari,
Here your are getting constraint violation exception this is due to pre existence of some records in student table. Set hbm2ddl to true and try it. Or delete all the records in all the tables. one more suggestion in student table you have mentioned primary key as college_Id it is not a good practise and why do you need element collection annotation it is for different purpose please remove it.
Regards,
Rama Krishna.

[Rama krishna]

[Rama krishna]

[Rama krishna]