CODEWITHSUNDEEP
grails
wwwclaes
wwwclaes

Reputation: 1152

Fetch only the ids from a hasMany in Grails?

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.

Upvotes: 0

Views: 255

Answers (3)

cubba9
cubba9

Reputation: 1

I used "Querying Associations" and "Projection" to do this in the Parent domain object. (Query - GORM for Hibernate):

class Parent {

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

    Collection<Long> getChildIds(){
        withCriteria {
            childs {
                projections {
                    property 'id'
                }
            }
            eq 'id', id
        }
    }

}

Upvotes: 0

tylerwal
tylerwal

Reputation: 1880

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.

Upvotes: 0

rcgeorge23
rcgeorge23

Reputation: 3694

You can do this with a projection. e.g.

def result = Child.createCriteria().list {
    projections {
        property('id')
    }
    eq ('parent', parent)
}

This will return just the ids of the child objects.

Upvotes: 2

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