Persisting Measurements¶

MeasurementField stores measurements in Django models. It persists the magnitude in a configurable base unit while tracking the input unit for display.

Declaring fields¶

from django.db import models
from general_manager.measurement import MeasurementField, Measurement

class Product(models.Model):
    weight = MeasurementField(base_unit="kg", null=True, blank=True)
    price = MeasurementField(base_unit="EUR", null=True, blank=True)

Assignments accept Measurement instances or human-readable strings:

product.weight = Measurement(750, "gram")
product.price = "19.99 EUR"

Base units¶

Choose base units that match your reporting needs. All stored values convert to the base unit automatically. When reading from the database, the original unit is restored so you can display the same unit the user provided.

Validation and forms¶

MeasurementField plugs into Django forms and admin just like other fields. Invalid strings raise ValidationError with descriptive messages. To customise form widgets, subclass MeasurementFormField or provide your own input parsing logic.

Migrations¶

Because measurements store magnitudes as decimals, they migrate cleanly across databases. If you change the base unit, run a data migration to rescale stored values.