PYTHON

django creating calculated fields in model

from django.db.models.functions import Concat
from django.db.models import Value, CharField

class OrderManager(models.Manager):
  def get_queryset(self):
      """Overrides the models.Manager method
         creates another callable field in orders model named 'link'
      """
      qs = super(OrderManager, self).get_queryset()
      .annotate(
        link=Concat(Value("<a href='#'>"), 'order_id', Value('</a>'), output_field=CharField()))
      return qs

class Order(models.Model):
    order_id = models.IntegerField(primary_key=True, null=False)
    # other fields  here 
    objects = OrderManager()