Domain classes to track Users and Games

Question

I'm trying to do something that seems so simple. I have a User class, and I have a Game class that matches up two Users. It's this simple:

class User {
    String username
    static hasMany = [games:Game]
}

class Game {
    User player1
    User player2
}

When I ran this, I got

Caused by GrailsDomainException: Property [games] in class [class User] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [user] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [games:'myprop']

So I did some digging and found mappedBy and changed my code to:

class User {
    String username
    static hasMany = [games:Game]
    static mappedBy = [games:'gid']
}

class Game {
    User player1
    User player2
    static mapping = {
        id generator:'identity', name:'gid'
    }
}

Now I get

Non-existent mapping property [gid] specified for property [games] in class [class User]

What am I doing wrong?

Answer 1

So here is probably what you want:

class User {

    static mappedBy = [player1Games: 'player1', player2Games: 'player2']

    static hasMany = [player1Games: Game, player2Games: Game]

    static belongsTo = Game
}

class Game {
    User player1
    User player2
}

Edit for new rules:

class User {
    static hasMany = [ games: Game ]
    static belongsTo = Game
}

class Game {
    static hasMany = [ players: User ]
    static constraints = {
        players(maxSize: 2)
    }
}