// The two observed requests (the team and its players)
let teamRequest = Team.filter(key: 1)
let playersRequest = Player.filter(Column("teamId") == 1)

// Two observations
let teamObservation = ValueObservation.trackingOne(teamRequest)
let playersObservation = ValueObservation.trackingAll(playersRequest)

// The combined observation
let observation = ValueObservation.combine(teamObservation, playersObservation)

// Start tracking players and teams
let observer = observation.start(in: dbQueue) { team: Team?, players: [Player] in
    print("Team or players have changed.")
}