django filter on the basis of text length

Question

I would like to filter my model on the basis of the length of the text Something like

MyModel.objects.filter(len(text) > 10)

where text

Answer 1

It would be much better and faster if you just add a column that pre-calculates(memoizes) the length of the text.

e.g.

class MyModel(models.Model):
    text = models.TextField()
    text_len = models.PositiveIntegerField()

     def save(self, *args, **kwargs):
         self.text_len = len(self.text)
         return super(MyModel, self).save(*args, **kwargs)

MyModel.objects.filter(text_len__gt = 10)     # Here text_len is pre-calculated by us on `save`