@Entity
@Table(name="MEASUREMENTS")
public class MeasurementsEntity {
   
   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   private Long id = -1L;
   
   @ManyToOne()//fetch=FetchType.EAGER)
   @JoinColumn(name="TYPE_ID")
   private MeasurementTypeEntity type = null;
   
   @ManyToOne(fetch=FetchType.EAGER,optional=false)
   @JoinTable(name="MEASUREMENTS_USER",
         joinColumns=@JoinColumn(name="MEASUREMENTS_ID"),
         inverseJoinColumns=@JoinColumn(name="USER_ID"))
   private UserEntity user = null;
   
   @OneToMany(cascade=CascadeType.ALL,mappedBy="measurements")
   @MapKeyColumn(name="DATE")
   @MapKeyTemporal(TemporalType.DATE)
   private Map<Date, MeasurementEntity> measurements = null;
   
   public MeasurementsEntity() {
      
   }
       
        // standard getters and setters follow...
}

@Entity
@Immutable
@Table(name="MEASUREMENT_TYPES")
public class MeasurementTypeEntity {
   
   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   private Long id = -1l;

   @Column(name="MEASUREMENT")
   protected String name = "";
   
   @ManyToOne(fetch=FetchType.EAGER)
   @JoinColumn(name="UNITS")
   protected UnitsEntity units = null;
   
   public MeasurementTypeEntity() {
      
   }

        // standard getters and setters follow...
}

measurements | CREATE TABLE `measurements` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `TYPE_ID` bigint(20) DEFAULT NULL,
  `type` bigint(20) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `FK74878437A55A5C7F` (`id`),
  KEY `FK74878437CD2C5E3D` (`type`),
  KEY `FK748784379A1CAF43` (`TYPE_ID`),
  CONSTRAINT `FK748784379A1CAF43` FOREIGN KEY (`TYPE_ID`) REFERENCES `measuremen
t_types` (`id`),
  CONSTRAINT `FK74878437A55A5C7F` FOREIGN KEY (`id`) REFERENCES `users` (`id`),
  CONSTRAINT `FK74878437CD2C5E3D` FOREIGN KEY (`type`) REFERENCES `measurement_t
ypes` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

   @Test
   public void testAllPersist() {
      if (u == null)
         Assert.fail("User info is null, failed to init.");
      TestBundle tb = makeTestBundle1();
      Session s = HibernateUtil.getSessionFactory().getCurrentSession();
      Transaction t = null;
      try {
         t = s.getTransaction();
         if (t == null || !t.isActive())
            t = s.beginTransaction();
         s.save(tb.getDimensionEntity());
         s.save(tb.getUnitsEntity());
         s.save(tb.getMeasurementTypeEntity());
         s.save(tb.getUserEntity());
         t.commit();
         s = HibernateUtil.getSessionFactory().getCurrentSession();
         t = s.beginTransaction();
                        // the exception is thrown on the following line.
         s.save(tb.getMeasurementsEntity()); // save parent, not table owner.
         s.save(tb.getMeasurementEntity()); // save child, table owner.
         t.commit();
      } catch (Exception e) {
         if (t != null && t.isActive())
            t.rollback();
         e.printStackTrace();
         Assert.fail("Failed due to exception "+e.getMessage());
      } finally {
         if (t != null && t.isActive())
            t.commit();
      }
   }

Hibernate: insert into DIMENSION (DIMENSION) values (?)
Hibernate: insert into UNITS (CONVERSION_FACTOR, DIMENSION_ID, UNITS) values (?, ?, ?)
Hibernate: insert into MEASUREMENT_TYPES (MEASUREMENT, UNITS) values (?, ?)
Hibernate: insert into USERS (USER_INFO) values (?)
Hibernate: insert into MEASUREMENTS (TYPE_ID) values (?)
org.hibernate.exception.GenericJDBCException: Field 'type' doesn't have a default value
   at org.hibernate.exception.internal.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:148)
   ... lots of irrelevant stack trace members, then...
   at com.knapptech.fitnesstracker.entities.TestUser.testAllPersist(TestUser.java:64)
   ... long stack trace ...
Caused by: java.sql.SQLException: Field 'type' doesn't have a default value
   ... long stack trace ...
org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:124)
   ... 57 more

@Entity
@Table(name="USERS")
public class UserEntity {
   
   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   private Long id = 0L;

   @ManyToOne(fetch=FetchType.EAGER,optional=false)
   @JoinColumn(name="USER_INFO",updatable=false,nullable=false)
   private UserInfoEntity userInfo = null;
   
   @OneToMany(mappedBy="measurements")
   @MapKeyJoinColumn(name="type")
   private Map<MeasurementTypeEntity, MeasurementsEntity> measurements = null;
   
//   @OneToMany
   @ElementCollection
   @JoinTable(name="USER_COMMENTS")
   @MapKeyColumn(name="DATE")
   @MapKeyTemporal(TemporalType.DATE)
   private Map<Date, String> comments = null;
   
   public UserEntity() {
      
   }