sample.py

class Smaple(models.Model):
    var_id = models.IntegerField()
    
    @cached_property
    def var(self):
        return Var.get(self.var_id)
        

class Var(models.Model):
    @classmethod
    def get(cls, pk):
        return cls.objects.get(pk=pk)
        

# pattern1        
vars = []
for sample in Sample.objects.all():
    l.appned(sample.var)
    

# petterns    
var_ids = [sample.var_id for sample in  Sample.objects.all()]
vars = Var.objects.in_builk(var_ids)