GORM one to one relationship while keeping existing entries

Question

After going over GORM's documentation, I've figured out how to create one-to-one relationships between objects. However, I haven't figured out how to go about enabling my desired relationship. The relationship I'm trying to create acts as a one-to-one, but keeps previous row entries for historical purposes.

For example, a Car can have multiple owners throughout its lifetime. If I have Car and Owner domain objects, how can I specify that the most recent entry in the Owners table for a given Car ID is the correct one?

Answer 1

There are lots of different ways to model this. IMO, one of the most flexible approaches is:

class User {
  String name
  static hasMany = [ownerships: Ownership]
}

class Car {
  String name
  static hasMany = [ownerships: Ownership]
}

class Ownership {
  Date start
  Date end
  static belongsTo = [owner: User, car: Car]
}

For example, when Ann sells her car to Bob, we set the end-time of Ann's Ownership record to the time of sale and save a new Ownership record for Bob with the start-time set to the time of sale.

If getting the current owner of a car is an operation we frequently need to perform, we could add a currentOwner method to Car

class Car {
  String name
  static hasMany = [ownerships: Ownership]

  Ownership currentOwner() {
    // depending on how this method is used, you might want to
    // return the User instead of the Ownership
    Ownership.findByEndIsNullAndCar(this)
  } 
}