Grails: Projection on many tables?

Question

I have some problems with projection in Grails. Could you please help me review them and suggest solutions for me?

1. I want to query data on many tables which has many-to-one relationship and projection on some properties on both of them. For example:

   class Person {
       int id
       String name
       String address
       static hasMany = [cars : Car]
   }
   
   class Car {
      int id
      String brand
      long price
      Person owner
      static belongsTo = [owner : Person]
   }
   

   So, how can I use just one query withCriteria (apply projection) to get information of a specified car (include brand, price, and the owner name)? Is it possible to use:

   Car.withCriteria {
        projections {
            property("brand")
            property("price")
            property("owner.name")
       }
       eq("id", carId)
   }
   

2. Can I use a projection to get information of one specified person along with name of all his cars? For example: [01, Perter, 01 Street A, [Mercedes, Toyota, Ducatti]]?

3. A special situation: (with above Person class)
   A person can join many Organization, and an Organization can have one "parent" Organizations (and vice versa, an Organization can have many other depend organizations). But there's a rule: a person just can join only one child organization of a given organization. So with a given organization O and a person P, what is the fastest way to get information of P along with the name of depended organization of O which has P as a member. I prefer to use Grails projection.

   Here's data model:

   class Person {
       int id
       String name
       String address
       static hasMany = [joinedOrgs : Organization] 
   }
   
   class Organization {
       int id
       String name
       Organization parentOrg
       static hasMany = [members : Person, childOrgs : Organization]
   }
   

I'm a newbie with Grails, and I'd like to understand GORM much more. Thank you so much for your help.

Answer 1

Try this

def results =  Car.createCriteria().list() { 
    createAlias('owner','owner')
    projections { 
        property('owner.name', 'owner.name') 
        property('brand','brand')
        property('price','price')
    }
}