I have a few classes similar to this example:

I want Hibernate to generate the schema for me, for everything else in my app it was worked great.

When it see two collection to the same class annotated with either @Many-to-Many or @CollectionOfElements it creates one table between User and Group with one column for each collection.

ie

The problem with this is that I cannot have either collection be empty. Since all of the columns are keys they are not allowed to be null.

Is there away to annotate this so they it creates separate tables or allows for nulls?

I have been beating on this all day, any help would be greatly appreciated.

Thanks,
Mike

I am having a similar problem. Is there an annotation that can be set so that Hibernate will create a separate map table for each Collection?

Thanks,
-Steve

The only I could think of to have Hibernate generate one table per collection would be to create different class for each collection:

ie




Then the user would look something like this:


But that would mean changing a lot of my existing objects and some of my business logic.

If there is no other way that's what I will do, but it seems like this could be done some other way.

So I tired my suggestion above of creating two abstract children and I have the same problem I started with.

Any help or ideas that I can try would be greatly appreciated.

Thanks,
Mike

First of all, I think you may need to convert your List declarations to Set. I have had issues with Hibernate saying it could not retrieve two bags simultaneously when I had multiple attributes of a class which were of type List as the collection class. Furthermore, a set actually is semantically correct. It would not make sense for a user to have the same Group object in either collection multiple times which a List would allow.

For your original issue, try explicitly specifying two join tables using annotations:

@ManyToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "ID")
@JoinTable(name = "USER_PRIMARY_GROUP_MAP",
joinColumns = @JoinColumn(name = "USER_ID"),
inverseJoinColumns = @JoinColumn(name = "GROUP_ID"))
protected Set<Group> primaryGroups = new LinkedHashSet<Group>() ;

@ManyToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "ID")
@JoinTable(name = "USER_SECONDARY_GROUP_MAP",
joinColumns = @JoinColumn(name = "USER_ID"),
inverseJoinColumns = @JoinColumn(name = "GROUP_ID"))
protected Set<Group> secondaryGroups = new LinkedHashSet<Group>() ;

NOTE: The above assumes that the USER and GROUP tables both are using ID as
their primary key column.

I have gotten away from using external hbm.xml mapping files but if you are using
the xml mapping files, I assume there is an equivalent mechanism for accomplishing
what the annotations above do.

Thanks for the reply.

I had it setup that way originally.

The problem with that is that this is class is the parent of many other classes so hibnerate puts constraints on all of the child tables. So I can never insert anything since no one mapping is going to exist in all of the child tables.

As far as List or Set agreed is should be set but its not my call :)

What I ended up doing was leaving it the way I had it but manually removing the "not null" on the two collection foreign keys. Seems to be working.