Question

Summary

I’m building a project in Django – and will many small-range positive decimal values (1.25, 0.01, etc). In the database (MySQL), it makes sense to store them as value*10^precision. This means instead of storing a float type (4 bytes), I can get away with a SmallInt(2 bytes). This is rad when it’s megabytes of data.

Problem
The issue is when Django and the PositiveSmallIntegerField() makes a widget that automatically checks for “whole number” values!

Option 1: Use a DecimalField() in the model code, and whenever the database changes, I update the SQL to be a SMALLINT(3).

PRECISION=2

class MyModule(models.Model):

    ...<fields>

    def readySave(self):
        pseudoDecimalField *= 10**PRECISION

    def setValues(self):
        pseudoDecimalField /= 10**PRECISION

    def save(self): 
        # pre-save things here
        self.readySave()
        super(MyModule, self).save()
        # post-save things here
        self.setValues()

Option 2: Use raw SQL commands when pushing/pulling values.

Any opinions or experiences on the matter are much appreciated. Does anyone have any other ways to make this happen?

Answer 1

The problem is only in “frontend” part, so there must be a way to solve the problem without modifying database. The neatest way to do that is to overwrite widget for the field in form. It should look like that:

class MyModuleForm(forms.Form):
    ....
    pseudoDecimalField = forms.PositiveSmallIntegerField(widget=forms.TextInput)

You can read more about widgets in great Django documentatin.