Unwanted GORM table creation

Question

I have two domain classes, Person and Workshop. A Workshop has an owner of type Person, and many participants of type Person. A Person can be the participant of many workshops. When enrolling people in workshops I want to do so from the Workshop side like workshop.AddToParticipants() so here is how I set up my domain classes.

class Person {
    String name

    static hasMany = [enrolledWorkshops: Workshop]
    static belongsTo = [Workshop]

}

class Workshop {
    Date startDate
    Date endDate
    String name

    Person owner
    static hasMany = [participants: Person]
}

GORM correctly creates a WORKSHOP_PARTICIPANTS table with WORKSHOP_ID and PERSON_ID columns, and adds an OWNER_ID column to the WORKSHOP table. This is all good.

However, it ALSO creates a WORKSHOP_OWNER table with PERSON_ID and OWNER_ID columns! This makes no sense to me, and no matter how I try changing the GORM relationships I just can't get it to work how I want without this annoying extra table being created. How can I prevent the WORKSHOP_OWNER table from being created? Any help is greatly appreciated! (if it is of any help, I am using Grails 2.3.7)

Answer 1

In order to get rid of the WORKSHOP_OWNER table you'd have to replace Person owner with static belongsTo = [owner: Person] in the Workshop class. But that would conflict with static belongsTo = [Workshop] in the Person class. Both can't be owners.

Try this:

class Person {
    String name
}

class Workshop {
    Date startDate
    Date endDate
    String name

    static belongsTo = [owner: Person]
    static hasMany = [participants: Participant]
}

class Participant {
    person person

    static belongsTo = [workshop: Workshop]
}

In the above example, a Person owns a Workshop, and a Participant is owned by a Workshop. The workshop table will get a owner_id to refer to the person, which gets rid of the workshop_owner table.

To add a Person to a Workshop you simply wrap it in a Participant

workshop.addToParticipants(new Participant(person: somePerson))

You'd loose the enrolledWorkshops property in Person, but you can accomplish the same thing with a query.

def workshops = Workshop.withCriteria {
    participants {
        eq 'person', somePerson
    }
}