title: Getting parent from child using JPA
body: <p>I have a phone object and a phone history object. I'd like to be able to retrieve a phone history object and then get its parent (phone), but for some reason, when I attempt to do this and then persist the child, I get an exception saying that phone_id isn't populated. Not sure how to fix this, although I suspect it has something to do with my mapping annotations. </p>
  
  <p>Below are my entity classes. I've tried changing the annotations to match the suggestion in the bidirectional relationships section here: <a href="http://docs.jboss.org/hibernate/annotations/3.5/reference/en/html/entity.html#entity-mapping-association" rel="nofollow">http://docs.jboss.org/hibernate/annotations/3.5/reference/en/html/entity.html#entity-mapping-association</a> but this didn't seem to do the trick. I'm new to JPA, so this is probably simple for someone with more experience, but I'm stumped. TIA.</p>
  
  <p>Phone entity:</p>
  
  <pre><code>package com.blah.model;
  
  import java.util.ArrayList;
  import java.util.Calendar;
  import java.util.List;
  
  import javax.persistence.CascadeType;
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.FetchType;
  import javax.persistence.GeneratedValue;
  import javax.persistence.Id;
  import javax.persistence.JoinColumn;
  import javax.persistence.ManyToOne;
  import javax.persistence.OneToMany;
  import javax.persistence.Table;
  import javax.persistence.Temporal;
  import javax.persistence.TemporalType;
  
  @Entity
  @Table(name = "phones")
  public class EPhone implements BaseModel {
  
      private static final long serialVersionUID = 3497994786207995664L;
  
      @Id
      @GeneratedValue
      @Column(name = "id")
      private Long id;
  
      @ManyToOne(fetch = FetchType.LAZY)
      @JoinColumn(name = "account_id",
              nullable = false)
      private EAccount account;
  
      @Temporal(TemporalType.TIMESTAMP)
      private Calendar created;
  
      @Column(name = "value",
          nullable = false)
          private Long value;
  
      @OneToMany(fetch = FetchType.LAZY,
              mappedBy = "phone",
              cascade = CascadeType.ALL)
      private final List&lt;EPhoneHistory&gt; history;
  
      public EPhone() {
          this(Calendar.getInstance());
      }
  
      public EPhone(final Calendar createdDate) {
          setCreated(createdDate);
          history = new ArrayList&lt;EPhoneHistory&gt;();
      }
  
      public void add(EPhoneHistory phoneHistoryItem) {
          history.add(phoneHistoryItem);
      }
  
      public EAccount getAccount() {
          return account;
      }
  
      public Calendar getCreated() {
          return created;
      }
  
      @OneToMany(fetch = FetchType.LAZY,
              mappedBy = "phone",
              cascade = CascadeType.ALL)
      public List&lt;EPhoneHistory&gt; getHistory() {
          return history;
      }
  
      public Long getId() {
          return id;
      }
  
      public Long getValue() {
          return value;
      }
  
      public void setAccount(EAccount account) {
          this.account = account;
      }
  
      public void setCreated(Calendar created) {
          this.created = created;
      }
  
      public void setId(Long id) {
          this.id = id;
      }
  
      public void setValue(Long value) {
          this.value = value;
      }
  
  }
  </code></pre>
  
  <p>Phone History entity:</p>
  
  <pre><code>package com.blah.model;
  
  import java.util.Calendar;
  
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.EnumType;
  import javax.persistence.Enumerated;
  import javax.persistence.FetchType;
  import javax.persistence.GeneratedValue;
  import javax.persistence.Id;
  import javax.persistence.JoinColumn;
  import javax.persistence.ManyToOne;
  import javax.persistence.Table;
  import javax.persistence.Temporal;
  import javax.persistence.TemporalType;
  
  @Entity
  @Table(name = "phone_history")
  public class EPhoneHistory implements BaseModel {
  
      private static final long serialVersionUID = 4591314258588732076L;
  
      @Id
      @GeneratedValue
      @Column(name = "id")
      private Long Id;
  
      @ManyToOne(fetch = FetchType.LAZY)
      @JoinColumn(name = "phone_id",
              nullable = false)
      private EPhone phone;
  
      @Temporal(TemporalType.TIMESTAMP)
      private Calendar created;
  
      @Enumerated(EnumType.ORDINAL)
      @Column(name = "type_id")
      private PhoneHistoryType type;
  
      public Calendar getCreated() {
          return created;
      }
  
      public Long getId() {
          return Id;
      }
  
      public EPhone getPhone() {
          return phone;
      }
  
      public PhoneHistoryType getType() {
          return type;
      }
  
      public void setCreated(Calendar created) {
          this.created = created;
      }
  
      public void setId(Long id) {
          Id = id;
      }
  
      public void setPhone(EPhone phone) {
          this.phone = phone;
      }
  
      public void setType(PhoneHistoryType type) {
          this.type = type;
      }
  
  }
  </code></pre>
  
  <p><strong>UPDATE for clarification (this is a test that fails):</strong></p>
  
  <pre><code>package com.blah.model.repository;
  
  import org.junit.Test;
  import org.springframework.beans.factory.annotation.Autowired;
  import org.springframework.transaction.annotation.Transactional;
  
  import com.blah.AbstractBaseDbTestCase;
  import com.blah.model.EPhoneHistory;
  import com.blah.model.PhoneHistoryType;
  
  public class PhoneHistoryRepositoryTest extends AbstractBaseDbTestCase {
  
      @Autowired
      PhoneHistoryRepository phoneHistoryRepo;
  
      @Test
      @Transactional
      public void testCreateAndSavePhoneHistory() {
  
          EPhoneHistory existingPhoneHistory = phoneHistoryRepo.find(1L);
  
          EPhoneHistory newPhoneHistory = new EPhoneHistory();
          newPhoneHistory.setType(PhoneHistoryType.VOICE);
  
          // I assume this is where I would
          // set the phone, but I don't have it.
          // existingPhoneHistory.setPhone(phone);
  
          // This is what I'm having trouble with. getPhone() doesn't populate the
          // phone field with the parent phone object.
          existingPhoneHistory.getPhone().add(newPhoneHistory);
  
          phoneHistoryRepo.persist(existingPhoneHistory);
          phoneHistoryRepo.flush();
      }
  }
  </code></pre>
  
  <p>And the failure stack trace:</p>
  
  <pre><code>org.springframework.dao.DataIntegrityViolationException: NULL not allowed for column "PHONE_ID"; SQL statement:
  insert into phone_history (id, created, phone_id, type_id) values (null, ?, ?, ?) [23502-168]; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: NULL not allowed for column "PHONE_ID"; SQL statement:
  insert into phone_history (id, created, phone_id, type_id) values (null, ?, ?, ?) [23502-168]
      at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:643)
      at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:104)
      at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:403)
      at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:58)
      at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:213)
      at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:163)
      at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
      at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
      at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
      at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:622)
      at com.blah.model.repository.PhoneHistoryRepository$$EnhancerByCGLIB$$4f90cdde.flush(&lt;generated&gt;)
      at com.blah.model.repository.PhoneHistoryRepositoryTest.testCreateAndSavePhoneHistory(PhoneHistoryRepositoryTest.java:29)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
      at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
      at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
      at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
      at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
      at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
      at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:30)
      at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
      at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
      at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)
      at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
      at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
      at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
      at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
      at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
      at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
      at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
      at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
      at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
      at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)
      at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
      at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
      at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
      at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
      at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
      at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
  Caused by: org.hibernate.exception.ConstraintViolationException: NULL not allowed for column "PHONE_ID"; SQL statement:
  insert into phone_history (id, created, phone_id, type_id) values (null, ?, ?, ?) [23502-168]
      at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:128)
      at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)
      at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125)
      at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110)
      at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:129)
      at org.hibernate.engine.jdbc.internal.proxy.AbstractProxyHandler.invoke(AbstractProxyHandler.java:81)
      at $Proxy37.executeUpdate(Unknown Source)
      at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:96)
      at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:58)
      at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2870)
      at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3381)
      at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:81)
      at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:362)
      at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:203)
      at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:183)
      at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:167)
      at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:320)
      at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:287)
      at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:193)
      at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:126)
      at org.hibernate.ejb.event.EJB3PersistEventListener.saveWithGeneratedId(EJB3PersistEventListener.java:78)
      at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:208)
      at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:151)
      at org.hibernate.internal.SessionImpl.firePersistOnFlush(SessionImpl.java:870)
      at org.hibernate.internal.SessionImpl.persistOnFlush(SessionImpl.java:863)
      at org.hibernate.engine.spi.CascadingAction$8.cascade(CascadingAction.java:346)
      at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:380)
      at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
      at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
      at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:409)
      at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:350)
      at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:326)
      at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:208)
      at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:165)
      at org.hibernate.event.internal.AbstractFlushingEventListener.cascadeOnFlush(AbstractFlushingEventListener.java:160)
      at org.hibernate.event.internal.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:151)
      at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:88)
      at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
      at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1214)
      at org.hibernate.ejb.AbstractEntityManagerImpl.flush(AbstractEntityManagerImpl.java:986)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:240)
      at $Proxy32.flush(Unknown Source)
      at com.blah.model.repository.AbstractRepository.flush(AbstractRepository.java:41)
      at com.blah.model.repository.AbstractRepository$$FastClassByCGLIB$$1ba8d45c.invoke(&lt;generated&gt;)
      at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:149)
      at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:689)
      at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
      at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:155)
      ... 36 more
  Caused by: org.h2.jdbc.JdbcSQLException: NULL not allowed for column "PHONE_ID"; SQL statement:
  insert into phone_history (id, created, phone_id, type_id) values (null, ?, ?, ?) [23502-168]
      at org.h2.message.DbException.getJdbcSQLException(DbException.java:329)
      at org.h2.message.DbException.get(DbException.java:169)
      at org.h2.message.DbException.get(DbException.java:146)
      at org.h2.table.Column.validateConvertUpdateSequence(Column.java:293)
      at org.h2.table.Table.validateConvertUpdateSequence(Table.java:689)
      at org.h2.command.dml.Insert.insertRows(Insert.java:120)
      at org.h2.command.dml.Insert.update(Insert.java:84)
      at org.h2.command.CommandContainer.update(CommandContainer.java:75)
      at org.h2.command.Command.executeUpdate(Command.java:230)
      at org.h2.jdbc.JdbcPreparedStatement.executeUpdateInternal(JdbcPreparedStatement.java:156)
      at org.h2.jdbc.JdbcPreparedStatement.executeUpdate(JdbcPreparedStatement.java:142)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:122)
      ... 83 more
  </code></pre>