JPA/Hibernate - Entity name seems to be important. If I rename to "Bob" works fine

Question

This one has had me stumped for several hours. It's related to my other question here:

JPA/hibernate - Cannot add or update a child row: a foreign key constraint fails - BUT record exists

I got rid of nearly all the code and narrowed down the problem. I have three very simple entities:

@Entity
public class Building {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    public Building() {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }
}

Other.java

@Entity
public class Other {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "building_id")
    private Building building;

    public Other() {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Building getBuilding() {
        return building;
    }

    public void setBuilding(Building school) {
        this.building = school;
    }
}

Event.java

@Entity
public class Event {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private long id;

    @ManyToOne
    @JoinColumn(name = "other_id")
    private Other other;


    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public Other getOther() {
        return other;
    }

    public void setOther(Other other) {
        this.other = other;
    }
}

This will fail with a foreign key constraint violation:

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`blah`.`event`, CONSTRAINT `FK403827A76D0546B` FOREIGN KEY (`other_id`) REFERENCES `Other` (`id`))
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)

NOW HERE'S THE REALLY BIZARRE PART!!!! If I do an eclipse refactor and rename the "Other" entity "Bob" it works perfectly fine. Just so we're on the same page, the Event entity will now look like this:

@Entity
public class Event {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private long id;

    @ManyToOne
    @JoinColumn(name = "bob_id")
    private Bob bob;


    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public Bob getBob() {
        return bob;
    }

    public void setBob(Bob bob) {
        this.bob = bob;
    }
}

And now it works perfectly fine. Can someone please explain this to a Hibernate newbie like myself? This really has me stumped. It fails when I persist a new Event to the database in my service layer:

@Transactional(propagation=Propagation.REQUIRED, rollbackFor=Exception.class) 
public void addEvent(Event event) throws ErrorCodeException, Exception
{
    // not sure if I need to do this, still fails if I remove it
    event.setOther(otherDAO.getReferenceById(event.getOther().getId()));
    eventDAO.persist(event);
}

One further comment. Instead of renaming Other to Bob, I can also set the table name to lowercase:

@Entity
@Table(name = "other")
public class Other {

This ALSO fixes it. But I cannot accept these solutions. I want to know why it's failing. I made a technology decision not to use Grails to avoid this type of "magic".

Here's the SQL hibernate logs:

// Initial database inserts
Hibernate: insert into Building values ( )
Hibernate: insert into Other (building_id) values (?)

// Insert which throws exception
Hibernate: insert into Event (other_id) values (?)
2011-06-27 11:31:51 JDBCExceptionReporter [WARN] SQL Error: 1452, SQLState: 23000
2011-06-27 11:31:51 JDBCExceptionReporter [ERROR] Cannot add or update a child row: a foreign key constraint fails (`blah`.`event`, CONSTRAINT `FK403827A76D0546B` FOREIGN KEY (`other_id`) REFERENCES `Other` (`id`))
org.springframework.orm.jpa.JpaSystemException: org.hibernate.exception.ConstraintViolationException: could not insert: [com.blah.server.domain.Event]; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: could not insert: [com.blah.server.domain.Event]

Answer 1

UPDATE: I found the solution here:

http://developmentality.wordpress.com/2011/05/23/hibernate-mysql-mac-foreign-key-nightmares-a-painless-solution-to-a-painful-problem/

It seems the combination of mysql, hibernate, and mac os x cause this problem. As a solution, use a lowercase naming strategy.