[Python] Limiting amount of objects user can add in another object

I just have a quick question: I would like to limit exercises in training unit to 3-5 exercises , and limit training units in training plan to 12 training units, so the user will not add an infinite number of exercises, or infinite number of training units in a plan?

class TrainingPlan(models.Model):
user= models.ForeignKey(User, on_delete=models.CASCADE)
nameoftheplan = models.CharField(verbose_name="Name of the plan",max_length=20, null=True)
Squat1RM = models.PositiveIntegerField(verbose_name="100%RM in squat",default=0, blank=True, null=True)
DeadliftT1RM =models.PositiveIntegerField(verbose_name="100%RM maximal repetition in deadlift",default=0, blank=True, null=True)
Benchpress1RM = models.PositiveIntegerField(verbose_name="100%RM maximal repetition in benchpress",default=0, blank=True, null=True)
mesocycle= models.CharField(max_length=40, choices=MESOCYCLE_CHOICES,default=MESOCYCLE_GPP)
timeoftheplan= models.CharField(max_length=40,choices=TIME_CHOICE,default=TIME_WEEK3 )

def __str__(self):
return str(self.nameoftheplan)

class TrainingUnit(models.Model):
trainingplan=models.ForeignKey(TrainingPlan, on_delete=models.CASCADE)


class Exercise(models.Model):
trainingunit=models.ForeignKey(TrainingUnit,on_delete=models.CASCADE)
exercisename=models.CharField(max_length=100,verbose_name="Exercise",choices=EXERCISE_CHOICES)
exercisesets=models.IntegerField(choices=SETSCHOICES)
exercisereps=models.IntegerField(choices=REPCHOICES)

Continue reading...