OneToMany ClassCastException configuration problem

ebessette · **Joined:** Fri Jan 18, 2008 1:59 pm **Posts:** 10

Hibernate version: 3.2
Name and version of the database you are using: MySQL 5

I'm trying to setup a one to many relationship, but only get one part of the "many" class instead of the entire object. Is this possible? Here's my code. If you have any ideas on how to do this, I'd really appreciate any help you can offer.

Code:

@Entity
@Table(name = "locations")
public class Location {
...
   @OneToMany(targetEntity = Type.class)
   @JoinTable(
      name = "locations_types", 
      joinColumns = @JoinColumn(name = "location_id"), 
      inverseJoinColumns = @JoinColumn(name = "type_id")
   )
   @OrderBy(value = "type")
   private List<String>      types;
...
}

@Entity
@Table(name = "types")
public class Type {

   @Id
   @ManyToOne(targetEntity=Location.class)
   private int      id;

   @Column
   private String   type;
...
}

Full stack trace of any exception that occurs:
java.lang.ClassCastException: com.package.path.model.Type

Thanks,
Eric

ebessette · **Joined:** Fri Jan 18, 2008 1:59 pm **Posts:** 10

After reading the documentation more, I realized that I should be using @CollectionOfElements instead. Like so:

Code:

@Entity
@Table(name = "locations")
public class Location {
...
   @CollectionOfElements
   @JoinTable(
      name = "types_with_location", 
      joinColumns = @JoinColumn(name = "location_id")
   )
   @Column(name = "type", nullable = false)
   @IndexColumn(name = "type_id")
   private List<String>      types;
...
} 

Where the "types_with_location" view is:

Code:

select 
   lt.location_id, 
   lt.type_id, 
   t.type 
from 
   types t join 
   locations_types lt on ( t.id = lt.type_id )

However, my types list is filled with a bunch of null values, in addition to the correct string values. Trying to figure that one out now.

Thanks,
Eric

carlolf · **Posted:** Sat Jun 14, 2008 12:25 pm

What you are doing seems very curious and odd to me!

ebessette wrote:

...
@OneToMany(targetEntity = Type.class)
@JoinTable(
name = "locations_types",
joinColumns = @JoinColumn(name = "location_id"),
inverseJoinColumns = @JoinColumn(name = "type_id")
)
@OrderBy(value = "type")
private List<String> types;

@Entity
@Table(name = "types")
public class Type {

@Id
@ManyToOne(targetEntity=Location.class)
private int id;
...
}
[/code]

First, you need not "targetEntity=" - if you would map to a

Code:

private List<Type> types;

,

and on the reverse side to

Code:

private Location loc;

- not to an id (the id is in the database, but not in Java code.

Remember: Hibernate and JPA are working on POJOs; so you just have to code bidirectional relations using Java objects on both sides!

Or, did I misunderstand your effort completely?

ebessette · **Joined:** Fri Jan 18, 2008 1:59 pm **Posts:** 10

I actually got it to work by removing all the nullable=false references and the @IndexColumn annotation. I'm really not sure why it works, but it does, so I'm happy. :)

Thanks,
Eric

Cameron McKenzie · **Posted:** Sun Jun 15, 2008 10:56 am

Well, thanks for the update. Maybe if you figure out why it works like that, you'll give an update as well. :)