Fetch only the ids from a hasMany in Grails?

Question

I know I can do Parent.childId in Grails, but is there anything similar I can do to only load ids (proxies) for every children in a hasMany? I.e., something similar to Parent.childrenIds?

In my case, the hasMany is mapped by a joinTable.

Answer 1

With a joinTable in mind:

def getChildIds(parentId) {
    Child.withSession { session -> 
        def sql = new Sql(session.connection())    
        sql.rows(
            'select pc.child_id from parent_child pc where pc.parent_id = :parentId',
             [parentId: parentId]
        ).collect{ it.child_id }
    }
}

This works for a joinTable mapped as such:

class Parent {

    static mapping = {
        childs joinTable: [name: 'parent_child', column: 'child_id', key: 'parent_id']
    }
    ...

It's not pretty but I believe it's the best way considering the situation and requirement.