how do i create a one to many (hibernate) relationship using jpa

I'm trying to persist  data into 2 tables which has one to many relationship
Child table has foreign key relationship with the parent table

I'm getting the following exception


avax.persistence.RollbackException: Error while commiting the
transaction
       at
org.hibernate.ejb.TransactionImpl.commit(TransactionImpl.java:71)
       at
com.csg.cs.pb.usa.hdt.model.test.QueryTest.testQuery2(QueryTest.java:78)
       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
       at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.jav
a:39)
       at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessor
Impl.java:25)
       at java.lang.reflect.Method.invoke(Method.java:585)
       at junit.framework.TestCase.runTest(TestCase.java:168)
       at junit.framework.TestCase.runBare(TestCase.java:134)
       at junit.framework.TestResult$1.protect(TestResult.java:110)
       at junit.framework.TestResult.runProtected(TestResult.java:128)
       at junit.framework.TestResult.run(TestResult.java:113)
       at junit.framework.TestCase.run(TestCase.java:124)
       at junit.framework.TestSuite.runTest(TestSuite.java:232)
       at junit.framework.TestSuite.run(TestSuite.java:227)
       at
org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.jav
a:79)
       at
org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4Tes
tReference.java:38)
       at
org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.ja
va:38)
       at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTe
stRunner.java:460)
       at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTe
stRunner.java:673)
       at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRun
ner.java:386)
       at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRu
nner.java:196)
Caused by: org.hibernate.exception.ConstraintViolationException: Could
not execute JDBC batch update
       at
org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java
:94)
       at
org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.
java:66)
       at
org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:275
)
       at
org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:266)
       at
org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:167)
       at
org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(
AbstractFlushingEventListener.java:321)
       at
org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEv
entListener.java:50)
       at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1027)
       at
org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:365)
       at
org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:13
7)
       at
org.hibernate.ejb.TransactionImpl.commit(TransactionImpl.java:54)
       ... 20 more
Caused by: java.sql.BatchUpdateException: ORA-01400: cannot insert NULL
into ("PBDT"."PROJECT"."ORGANIZATION_ID")

       at
oracle.jdbc.dbaccess.DBError.throwBatchUpdateException(DBError.java:459)
       at
oracle.jdbc.driver.OraclePreparedStatement.executeBatch(OraclePreparedSt
atement.java:4133)
       at
org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:7
0)
       at
org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:268

package test.model;
 
 
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
 
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.OneToMany;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
 
@Entity
@Table(name = "ORGANIZATION")
@SequenceGenerator(name = "orgSeq", sequenceName = "HDT_DEAL_SEQ")
public class Organization implements Serializable {
       @Id
       @Column(name="ORGANIZATION_ID")
 @GeneratedValue(generator = "orgSeq", strategy =
GenerationType.SEQUENCE)
       private Integer id;
 
       private String name;
 
 @OneToMany(cascade = CascadeType.ALL,   mappedBy = "organization")
 
       private List<Project> projectCollection;
 
       private static final long serialVersionUID = 1L;
 
       public Organization() {
               super();
       }
 
       public Organization(String string) {
   this.name=string;
 }
 
 public Integer getId() {
               return this.id;
       }
 
       public void setId(Integer organizationId) {
               this.id = organizationId;
       }
 
       public String getName() {
               return this.name;
       }
 
       public void setName(String name) {
               this.name = name;
       }
 
       public List<Project> getProjectCollection() {
               return this.projectCollection;
       }
 /**
  * add a new project
  * @param project
  */
 public void addProject(Project project){
   if(projectCollection == null) projectCollection = new
ArrayList<Project> ();
   //liability.setPayer(this);
   projectCollection.add(project);
 }
 
       public void setProjectCollection(List<Project>
projectCollection) {
               this.projectCollection = projectCollection;
       }
 
}
 
 
 
 
 
 
 
 
 
 
 
package test.model;
 
 
import java.io.Serializable;
 
import javax.persistence.Column;
import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
 
@Entity
@Table(name = "PROJECT")
@SequenceGenerator(name = "projSeq", sequenceName = "HDT_SEQ")
public class Project implements Serializable {
       @Id
       @Column(name="PROJECT_ID")
 
 @GeneratedValue(generator = "projSeq", strategy =
GenerationType.SEQUENCE)
       private Integer id;
 
       private String name;
 
       @ManyToOne
       @JoinColumn(name="ORGANIZATION_ID")
       private Organization organization;
 
       private static final long serialVersionUID = 1L;
 
       public Project() {
               super();
       }
 
       public Project(String string) {
  this.name=string;
 }
 
 public Integer getId() {
               return this.id;
       }
 
       public void setId(Integer projectId) {
               this.id = projectId;
       }
 
       public String getName() {
               return this.name;
       }
 
       public void setName(String name) {
               this.name = name;
       }
 
       public Organization getOrganization() {
               return this.organization;
       }
 
       public void setOrganizationId(Organization organization) {
               this.organization = organization;
       }
 
}
 
 
 
 
//This is the test method
 
 
 public void testQuery2() {
  this.em = entityManagerFactory.createEntityManager();
   em.getTransaction().begin();
   Organization organization = new Organization(
       " The Apache Software");
List<Project> projectCollection = new ArrayList<Project>();
   Project project = new Project("Streaming LOB support (for
OpenJPA)");
   organization.addProject(project);
 //   projectCollection.add(project);
  // project = new Project("Maven Dependency Visualization");
   //projectCollection.add(project);
   //organization.setProjectCollection(projectCollection);
 
  // organization.getProjectCollection().addAll(projectCollection);
   //organization.getProjectCollection.(projectCollection);
   em.persist(organization);
 
   em.getTransaction().commit();

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