Django - 如何在保存新对象时获取 self.id? [英] Django - How to get self.id when saving a new object?

问题描述

我的一个模型有问题.我正在上传图像，我想存储 id(数据库表中的 pk)，但我需要知道 Django 何时可以访问 self.id.

I have a problem in one of my models. I'm uploading an image, and I want to store the id (pk in the database table) but I need to know at which point Django will have access to self.id.

models.py

class BicycleAdItemKind(MPTTModel):
    def url(self, filename):
        pdb.set_trace()

        url = "MultimediaData/HelpAdImages/ItemKind/%s/%s" % (self.id, filename)
        return url

    def item_kind_image(self):
        return '<img align="middle" src="/media/%s" height="60px" />' % self.image
    item_kind_image.allow_tags = True     

    # Bicicleta completa, Componentes para bicicleta, Acessorios para ciclista
    n_item_kind      = models.CharField(max_length=50) 
    parent           = TreeForeignKey('self', null=True,
                                      blank=True, related_name='children')
    description      = models.TextField(null=True, blank=True)
    image            = models.ImageField(upload_to=url, null=True, blank=True)
    date_inserted    = models.DateTimeField(auto_now_add=True)
    date_last_update = models.DateTimeField(auto_now=True)

    def __unicode__(self):
        return self.n_item_kind

    class MPTTMeta:
        order_insertion_by = ['n_item_kind']

问题出在url()方法上；我只能在更新对象时获得 self.id ，在创建新对象时我没有获得 self.id .如何修改此模型，以便在创建新对象时获得 self.id?

The problem is in the url() method; I can only get self.id when updating an object, I don't get the self.id when creating a new object. How can I modify this model so that I get self.id when creating a new object?

使用当前代码，当我创建一个新对象时，我最终会得到一个像这样的网址:

With the current code, when I'm creating a new object I will end up with a url like:

MultimediaData/HelpAdImages/ItemKind/None/somefile.jpg

我需要有类似的东西:

MultimediaData/HelpAdImages/ItemKind/35/somefile.jpg

有什么线索吗?

推荐答案

如果是新建对象，需要先保存再访问self.id，因为

If it's a new object, you need to save it first and then access self.id, because

"There's no way to tell what the value of an ID will be before you call save(), 
 because that value is calculated by your database, not by Django."

查看django的文档https://docs.djangoproject.com/en/dev/ref/models/实例/

Check django's document https://docs.djangoproject.com/en/dev/ref/models/instances/

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