1json.id workout.id
 2json.body_weight workout.body_weight
 3json.routine_name workout.routine.name
 4json.exercises workout.sets.includes(:exercise).order(:created_at).group_by(&:exercise) do |exercise, sets|
 5  json.id exercise.id
 6  json.name exercise.name
 7  json.sets sets.sort_by(&:created_at) do |set|
 8    json.partial! 'sets/set', set: set
 9  end
10end