final class HomeTeam: ModelAlias {
    static let name = "home_teams"
    let model = Team()
}
final class AwayTeam: ModelAlias {
    static let name = "away_teams"
    let model = Team()
}
 
/// Find games that were popular enough for the crowd to be larger
/// than the number of players playing it.        
Match.query(on: self.database)
    .join(HomeTeam.self, on: \Match.$homeTeam.$id == \HomeTeam.$id)
    .join(AwayTeam.self, on: \Match.$awayTeam.$id == \AwayTeam.$id)
    /// You can currently conditionally filter the originally 
    /// queried Model type if types match (in this case,  
    /// crowd size and total players would be of type Int)
    .filter(\Match.$crowd, .greaterThan, \Match.$totalPlayers)
    .all()

Match.query(on: self.database)
    .join(HomeTeam.self, on: \Match.$homeTeam.$id == \HomeTeam.$id)
    .join(AwayTeam.self, on: \Match.$awayTeam.$id == \AwayTeam.$id)
    /// Here you can filter a ModelAlias according to properties shared with 
    /// another ModelAlias of the same original Model type.
    .filter(\HomeTeam.$score, .greaterThan, \AwayTeam.$score)
    .all()

    /// Please note this code is for demonstration only 
    /// and is not functional.
    @discardableResult
    public func filter<Left, Right>(
        _ lhsField: KeyPath<FirstModelAlias, Left>,
        _ method: DatabaseQuery.Filter.Method,
        _ rhsField: KeyPath<SecondModelAlias, Right>
    ) -> Self
        where Left: QueryableProperty,
            Left.Model == FirstModelAlias,
            Right: QueryableProperty,
            Right.Model == SecondModelAlias
    {
        self.filter(FirstModelAlias.path(for: lhsField), method, SecondModelAlias.path(for: rhsField))
    }