I have some interconnected entities:

• exercises, for instance push ups, pull ups, squats. Each exercise has a name, the muscles involved (chest, legs …), the executions steps and the category type.

• exercise category is an enum that represents how is this exercise
  measured. For instance “push up” is a “bodyweightReps” type as you
  need to measure only the repetitions performed. “Barbell squat” is a
  “weightReps” type as you record both weight on the barbell and the
  repetitions performed. Each exercise can therefore be measured with
  different parameters and with a different number of parameters
  (“bodyweightReps” needs to record only 1 parameter “repetition”,
  while “weightReps” needs 2, 1 for weight and 1 for repetition). For
  the moment all exercises can be measured with maximum 2 parameters,
  but that could change in the future

• workout activity, is an activity performed in a workout. It has an exercise, some notes and a list of workout sets performed

• workout set, a set of a workout activity. It has a rest time and a list of measures for the values stored (for instance number of repetitions performed, weight used …). The measures of the workout set depends on the parent Workout activity Exercise Category, as a set of a Workout Activity with “Barbell Squat”, needs to measure the weight and the repetitions performed, as the exercise category is “weightReps”.

As you can see, a WorkoutActivity has an exercise, and the structure of the child WorkoutSet measures property depends on the parent WorkoutActivity Exercise category property.

enum ExerciseType {
 weightReps,
 bodyWeightReps,
 distance,
 time
}

class Exercise {
 String name;
 List<String> executionSteps;
 ExerciseType category;
}

class Workout {
 String name
 List<WorkoutActivity> activities;
}

class WorkoutActivity {
 String note;
 Exercise exercise;
 List<WorkoutSet> sets;
}

class WorkoutSet {
 int restTime;
 List<double> measures;
}

The problem is that the above structure doesn’t guarantee that the WorkoutSets of a workout activity whose exercise category type is “bodyweightReps” have only one measure nor that if the category type is “weightReps” they have 2 measures. This issue raises some connected problems that can’t be ignored.

Is there a better way to structure the entities so that the measures of the child WorkoutSet can be forced to follow the parent Workout Activity Exercise Category type structure?