Hibernate: simple JOIN

[K.]

Hey!

I hope you can help me with my obviously simple problem. :)

I am using the Dropwizard Framework with the integrated hibernate to access a MySQL database and now I would like to do a simple JOIN.

I think it is good to break down the problem to a simple Room<-->Person example:
So, given the following sample table structure with Person(ID,ROOM_ID) and ROOM(ID,NAME):

[SQL]
CREATE TABLE IF NOT EXISTS `PERSON` (
  `ID` VARCHAR(100) NOT NULL,
  `ROOM_ID` INT NULL,
  PRIMARY KEY (`ID`))
ENGINE = InnoDB;

CREATE TABLE IF NOT EXISTS `ROOM` (
  `ID` INT NOT NULL AUTO_INCREMENT,
  `NAME` VARCHAR(45) NULL,
  PRIMARY KEY (`ID`))
ENGINE = InnoDB;
[/SQL]

... I would like to join PERSON p with ROOM r ON p.ROOM_ID=r.ID. --> NOTHING special at all :(
Of course, pure SQL works:

[SQL]
SELECT p.ID,r.NAME FROM PERSON p INNER JOIN ROOM r ON p.ROOM_ID=r.ID
[/SQL]

So, since I am using Hibernate, there are two sample POJOs:

[JAVA]
@Entity
@Table(name = "PERSON")
@NamedQuery(name = "...", query = "SELECT p,r FROM Person p INNER JOIN FETCH p.room r")
public class Person
{
    @Id
    @Column(name = "ID")
    private String ID;

    @ManyToOne(targetEntity = Room.class)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "ID")
    private Room room;
   
    //getter, setter, stuff :)
}

@/*just to clarify:*/javax.persistence.Entity
@Table(name = "ROOM")
public class Room
{
    @Id
    private int ID;

    @Column(name = "NAME")
    private String NAME;

    @OneToMany(targetEntity = Person.class)
    @JoinColumn(name = "ROOM_ID")
    private Set<Person> persons;

    //again ... getter, setter, stuff
}
[/JAVA]

And when I start the Dropwizard project, there occurs the following error:

org.hibernate.AnnotationException: Use of @OneToMany or @ManyToMany targeting an unmapped class com.bla.bla.Room.persons[this.is.shit.isn't.it.Person]

So, what are the problems? :)

[mve...@gmail.com]

This looks like a hibernate specific issue vs a dropwizard issue. 

Matt

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[K.]

Yes, after hours of googling it seems that something is wrong with the hibernate configuration. But since there are no standard hibernate configurations xml-files in Dropwizard, I think it might suit better in this group :) I can't imagine that I am the first Dropwizard user who needs to perform a JOIN withe hibernate ^^

[Carlo Barbara]

My guess based on this garbled error "org.hibernate.AnnotationException: Use of @OneToMany or @ManyToMany targeting an unmapped class com.bla.bla.Room.persons[this.is.shit.isn't.it.Person]", I would say that one of the two entities in the relationship haven't been added to the list of classes used to initialize the hibernate bundle.

[K.]

Hm, I thought that too :( But it looks good:

[JAVA]
private final HibernateBundle<ApiConfiguration> hibernate_person = new HibernateBundle<ApiConfiguration>(
        Person.class) {
    @Override
    public DataSourceFactory getDataSourceFactory(
        ApiConfiguration configuration)
    {
        return configuration.getDataSourceFactory();
    }

    };

private final HibernateBundle<ApiConfiguration> hibernate_room = new HibernateBundle<ApiConfiguration>(
        Room.class) {
    @Override
    public DataSourceFactory getDataSourceFactory(
        ApiConfiguration configuration)
    {
        return configuration.getDataSourceFactory();
    }

    };

@Override
    public void initialize(Bootstrap<ApiConfiguration> bootstrap)
    {
//...
    bootstrap.addBundle(hibernate_person);
    bootstrap.addBundle(hibernate_room);
//...
}
[/JAVA]

[Ramakrishna Nalam]

Why are there different hibernate bundles for different classes!

Please use the same bundle if you want to do things like joining across them.

The HibernateBundle constructor can take in multiple classes, so just pass in both the classes you have to it. That's one mistake I see.

Different bundles would probably be for use case where you want to connect to different db's.

Regards,
Rama.

[K.]

Oups, thank you! That was a good suggestion :) I really thought I have to use multiple HibernateBundles.