1json.id workout.id
 2json.body_weight workout.body_weight
 3json.occurred_at workout.occurred_at
 4json.routine_name workout.routine.name
 5json.exercises workout.sets.includes(:exercise).order(:created_at).group_by(&:exercise) do |exercise, sets|
 6  json.id exercise.id
 7  json.name exercise.name
 8  json.sets sets.sort_by(&:created_at) do |set|
 9    json.partial! 'api/sets/set', set: set
10  end
11end