python - Tango with Django (v1.9/1.10) - 第 5 章，populate_rango 问题

Question

我会尽量简洁。这个问题的背景是我熟悉 Python，但是我对 django 是全新的。这本书是我第一次接触它，随着我对这本书的研究越来越多，我发现 django 的在线问答不是很笼统，因此很难“只用谷歌搜索”并找到答案。

我的环境

资源:Tango with Django(1.9/1.10版本)
发行版:基本操作系统，已修补到最新版本
Python版本:3.5
Django 版本:1.11.x

我的问题

我的错误是什么:django.core.exceptions.FieldError
详细信息是什么:模型页面的字段名称无效:“类别”。
错误是什么意思？:根据 The Docs , 当模型中的某个字段出现问题时会引发此错误..的 列出的原因以下看起来与我的问题相关:

死循环是由排序引起的。

我已经验证了模型中声明字段的顺序与 add_page 的顺序一致。同样，我调试了我的代码，发现所有字段在通过各种函数时看起来都是正确的。但是我在想也许 [this] 可能是问题所在。我认为作品“类别”以某种方式引用了类别类别？总故障排除猜想。

字段名称无效

它总是很简单，我已经检查过了并且变量的命名和用法在整个代码中是一致的。我还根据本书仔细检查了我的代码。一切似乎都井井有条，只是代码无法正常工作。

回溯

Traceback (most recent call last):
  File "/home/dj/opt/pycharm-2017.2.3/helpers/pydev/pydevd.py", line 1599, in <module>
    globals = debugger.run(setup['file'], None, None, is_module)
  File "/home/dj/opt/pycharm-2017.2.3/helpers/pydev/pydevd.py", line 1026, in run
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File "/home/dj/opt/pycharm-2017.2.3/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "/home/dj/Code/tango-with-django-book/workspace/tango_with_django_project/populate_rango.py", line 83, in <module>
    populate()
  File "/home/dj/Code/tango-with-django-book/workspace/tango_with_django_project/populate_rango.py", line 59, in populate
    add_page(c, p["title"], p["url"])
  File "/home/dj/Code/tango-with-django-book/workspace/tango_with_django_project/populate_rango.py", line 68, in add_page
    p = Page.objects.get_or_create(category=cat, title=title)[0]
  File "/usr/local/lib/python3.5/dist-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/django/db/models/query.py", line 459, in get_or_create
    lookup, params = self._extract_model_params(defaults, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/django/db/models/query.py", line 534, in _extract_model_params
    "', '".join(sorted(invalid_params)),
django.core.exceptions.FieldError: Invalid field name(s) for model Page: 'category'.

populate_rango.py

import os

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'tango_with_django_project.settings')

import django
django.setup() #imports Django projects settings into the context of this script

from rango.models import Category, Page

def populate():
    # First, we will create lists of dictionaries containing the pages we want to add
    # into each category.
    # Then, we will create a dictionary of dictionaries for our categories. 
    # This might seem a little bit confusing, but it allows us to iterate through each data structure, 
    # and add the data to our models. 


    # List of Dictionaries of "Python" Category pages... Tile:value, URL:value
    python_pages = [
        {"title": "Official Python Tutorial", "url": "https://docs.python.org/2/tutorial/"},
        {"title": "How to think like a Computer Scientist" ,"url": "http://www.greenteapress.com/thinkpython/"},
        {"title": "Learn python in Ten Minutes" ,"url": "https://www.korokithakis.net/tutorials"}
    ]

    # List of Dictionaries of "django" Category pages... Title:value, URL:value
    django_pages = [
        {"title":"Official Django Tutorial" ,"url":"https://docs.djangoprojects.com/en/1.11/intro/tutorial01/"},
        {"title":"Django Rocks" ,"url":"https://www.djangorocks.com"},
        {"title":"How to Tango with Django" ,"url":"https://tangowithdjango.com/"}
    ]

    # List of Dictionaries of "Other" Category pages... Title:value, URL:value
    other_pages = [
        {"title":"Bottle" ,"url":"http://bottlepy.org/docs/dev/"},
        {"title":"Flask" ,"url":"http://flask.pocoo.org/"}

    ]

    # A Dictionary of Categories. Passing the pages defined above to the "pages" attribute (making a page) and then applything the tag to which their definied
    # category. 
    cats = {
        "Python": {"pages": python_pages},
        "Django": {"pages": django_pages},
        "Other Frameworks": {"pages": other_pages}
    }

    # If you want to add more categories or pages, add them to the 
    # dictionaies above. 

    # The code below goes through the cats directory, then adds each category. 
        # and then adds all the associated pages for that category.
        # if you are using python 2.x then use cat.iteritems() see
        # https://docs.quantifiedcode.com/python-anti-patterns/readability
        # for more information about how to iterate over a dictionary properly

    for cat, cat_data in cats.items():
        c = add_cat(cat)
        for p in cat_data["pages"]:
            add_page(c, p["title"], p["url"])

    # Print out the categories we have added.    
    for c in Category.objects.all():
        for p in Page.objects.filter(category=c):
            print("- {0} - {1}".format(str(c), str(p)))


def add_page(cat, title, url, views=0):
    p = Page.objects.get_or_create(category=cat, title=title)[0]
    p.url = url
    p.views = views
    p.save()
    return p


def add_cat(name):
    c = Category.objects.get_or_create(name=name)[0]
    c.save()
    return c


if __name__ == '__main__':
    print("Starting Rango Population script...")
    populate()

模型.py

from django.db import models


# Create your models here.
class Category(models.Model):
    name = models.CharField(max_length=128, unique=True)

    class Meta:
        verbose_name_plural = 'Categories'

    def __str__(self):
        return self.name


class Page(models.Model):
    Category = models.ForeignKey(Category)
    title = models.CharField(max_length=128)
    url = models.URLField()
    views = models.IntegerField(default=0)


    def __str__(self):
        return self.title

不管怎样，即使我重建数据库，这个问题仍然存在。 (rm app.db, makemigrations, 迁移)

Answer 1

class Page(models.Model):
    Category = models.ForeignKey(Category)

变量名称区分大小写 - 这包括字段名称和其他类属性。将 Category = models.ForeignKey(Category) 更改为 category = models.ForeignKey(Category) 以适应 model coding style然后重建您的数据库表，您应该可以执行 Page.objects.get_or_create(category=cat...