Django模型-创建后更新对象属性

Question

I am working on some Django project (first time) and after lot of searching i have no clue how to proper update object attribute after creation. I have sucha models.py

    from django.db import models
import os


# Create your models here.

class Place(models.Model):
    # Build paths inside the project like this: os.path.join(BASE_DIR, ...)
    BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
    # Add templates folder for dynamic usage, os independent
    TEMPLATE_DIR = os.path.join(BASE_DIR, "templates/places")

    name = models.CharField(max_length=100, unique=True)
    display_name = models.CharField(max_length=100)
    floor = models.DecimalField(max_digits=3, decimal_places=0)
    template = models.FilePathField(path=TEMPLATE_DIR, match=".*html")
    url = models.URLField(unique=True)

# Display name of object in object list view
    def __str__(self):
        return self.name

Question is how to update url attribute after object creation of url to this particular object, it should be something like (base url + object_id i know object_id is created after object creation) but after searching documentation i dont have ideas how to do this properly.

I tried get_absolute_path but with no success.

Maybe some kind post_save method override ?

Answer 1

One option would be to override the model save method and detect if the model instance is being added or updated and update the url field accordingly:

class Place(models.Model):
    # ...
    def save(self, *args, **kwargs):
        is_adding = self._state.adding
        super(Place, self).save(self, *args, **kwargs)

        if is_adding:
            url = os.path.join(self.TEMPLATE_DIR, str(self.pk))
            super(Place, self).save(self, *args, **kwargs)

However, you needn't actually store the url as you can derive the value from other model fields when required. Hence, you can delete the url field and create a url method instead:

class Place(models.Model):
    # ...
    @property
    def url(self):
        return os.path.join(self.TEMPLATE_DIR, str(self.pk))

Here, the @property decoration here allows you to access place.url as if it was a model field.

Answer 2

This might be a good time to introduce something like Django celery into you're project and run this task async after creation.

You could have a task in a file like this:

# I'm making assumptions on project architecture..
from app.places import Place
from app.places.utils import PLACE_BASE_URL

@shared_task
def task_update_place_url(place_id):
    """ 
    Simple method to update Place url after creation. 
    """
    place = Place.objects.get(pk=place_id)
    place.url = PLACE_BASE_URL + place_id
    place.save()

Then inside of your view when you create your Place you can do this:

import json
from django.http.response import HttpResponse

from app.places.models import Place
from app.places.tasks import task_update_place_url

def create_place(request):
    """ 
    Creates a new Place and update url in task 
    """
    data = json.loads(request)
    place = Place.objects.create(**data)
    task_update_place_url.delay(place.id)
    return HttpResponse("Finished")