Django Calculated fields Save()-CodePudding

This is very basic, but I'm having trouble finding the correct way to do this. I would like to have fields that are calculated and saved into the database. In the example, cHpd,cMpd and cBph are all fields that are calculated in the calc_rates function. I am piecing together how to do this.

class Route(models.Model):
    rtNumber = models.CharField(max_length = 5)
    rtState = models.CharField(max_length = 2)
    rtOffice = models.CharField(max_length = 255)
    #stDate = models.DateField(blank=True)
    #edDate = models.DateField(blank=True)
    llcName = models.CharField(max_length =255)
    boxes = models.IntegerField(null=True)
    miles = models.IntegerField(null=True)
    hours = models.IntegerField(null=True)
    wrkDays = models.IntegerField(null=True)
    activeCont= models.BooleanField(default=None)
    contRate = models.IntegerField(null=True)
    cHpd = models.IntegerField(null=True)
    cMpd = models.IntegerField(null=True)
    cBph = models.IntegerField(null=True)


    @property
    def calc_rates(self):
        hpd = self.hours / self.wrkDays
        mpd = self.miles / self.wrkDays
        bph = self.boxes / hpd

        self.cHpd = hpd
        self.cMpd = mpd
        self.cBph = bhp

        super(Route, self).save()

CodePudding user response：

You need a Model property for each calculated field, like so:

@property
def hpd(self):
    return self.hours / self.wrkDays

@property
def mpd(self):
    return self.miles / self.wrkDays

@property
def bph(self):
    return self.boxes / self.hpd

CodePudding user response：

If you want to save it in the database you can use signals. Then it will be calculated everytime you run .save() on the model.

from django.db.models.signals import pre_save
from django.dispatch import receiver

@receiver(pre_save, sender=Route)
def my_callback(sender, instance, *args, **kwargs):
    instance.hpd = instance.hours / instance.wrkDays

But, there's really no point in saving it in the database in my opinion, I would remove the fields cHpd etc. and use the solution that Lewis provided.