Hibernate bit for entity mapping

I am trying to map the Java normalized model to the legacy database schema using Hibernate 3.5. One particular table encodes foreign keys on a one-to-many basis as a column of a bit array.

Consider the tables person

and club

that describe how people join clubs:

person: .----.------.    club: .----.---------.---------------------------.
        | id | name |          | id |   name  | members | binary(members) |
        |----+------|          |----+---------|---------+-----------------|
        |  1 | Bob  |          | 10 | Cricket |       0 |             000 |
        |  2 | Joe  |          | 11 | Tennis  |       5 |             101 | 
        |  3 | Sue  |          | 12 | Cooking |       7 |             111 |   
        '----'------'          | 13 | Golf    |       3 |             100 |
                               '----'---------'---------'-----------------'

      

        
        
        
      

    

So hopefully it's clear what is person.id

used as the bit index in the bit array club.members

:

.---.---.---.
| S | J | B |
| u | o | o |
| e | e | b |
|---+---+---|
| 1 | 0 | 1 |
'---'---'---'

      

        
        
        
      

    

In this example, the column members

tells us that:

• Nobody enters Cricket --- no flags set
• Bob / Sue → Tennis --- flags in positions 1 and 3 are set
• Bob / Sue / Joe → Cooking --- flags at positions 1, 2 and 3 are set
• Sue → Golf --- flag in position 3 is set

Now, a join table could be used for this example, which would simplify things and avoid many potential problems - for example: a maximum range members

that sets an upper bound on the number of rows people

. However, I am stuck with this circuit and it seems that there are factors in favor of using a bit array column back when.

In my Java domain, I would like to simulate this schema with objects like this:

class Person {
    private int id;
    private String name;
    ...
}

class Club {
    private Set<Person> members;
    private int id;
    private String name;
    ...
}

      

        
        
        
      

    

I am guessing that I should use the implementation UserType

, but could not find any examples where the items described by the user type are entity references rather than literal field values ​​or their composites. Also, I know I will need to consider how the objects person

are retrieved when the instance is loaded club

.

Can anyone tell me how I can tame this legacy schema using Hibernate?

Update

I recently had to revisit this display type in an old database. This time, it became apparent that our table equivalent members

was actually a static set and could be hard-coded as Enum

. With this simplification, it was quite easy to implement Hibernate UserType

converting between a bitmap and a set of enums.