This question is in two parts, first part is about clearing a list and second part is about assigning an owner to an object.

I have a one-to-many relationship between two domain objects in my model in Grails. The relationship looks like this...

```
class Person {

    static hasMany = [authorities: Role, locations: Location]
}

class Location {

    static belongsTo = Person

}

```

In my app the `locations` list on `Person` gets completely refreshed and replaced with a new list on a user action. What's more I get the list of `Location` objects independent of the associated `Person`. I resolve which person to apply them to by retrieving the currently logged in user, which I call `activePerson` and is fine for my purposes.

What I want to do is delete all the existing locations on `activePerson` and insert all the new ones, associating them with the `activePerson` as I go. I have a bunch of properties on `Person` which I don't want to persist at this point, so I want to avoid saving the whole parent object just because locations children have changed.

I thought of iterating throught the `activePerson.locations` list and deleting them one by one and relying on GORM/Hibernate to batch the queries together and flush at the end. This seems like brute force, although it might work. I was expecting there to be a `clearLocations` method or something similar, but I can't find one.

If I do just replace the `activePerson.locations` with a new list and call `activePerson.save(flush:true)`, will GORM handle the delete of the existing rows?

Secondly I want to put the new `Location` objects onto `activePerson`. Again I could populate the `activePerson.locations` and save the whole thing, but I would like to avoid that if I can. I can save them individually, but how do I set `belongsTo` on each `Location` object as I go?

So to recap:

1. How do I clear a list at the many end of a one-to-many collection?
2. How do I associate independent objects with a parent object and persist them individually?

Thanks