I will try to be concise. The background for this issue is that I’m familiar with Python, however I am BRAND NEW to django. This book is my first exposure to it and I’ve come to find the more I work through the book that online Q/A’s for django are not very general, thus making it harder to “just google it” and find an answer.
- MY ENVIRONMENT
Resource: Tango with Django (for version 1.9/1.10)
Distro: Elementary OS, Patched to the latest
Python Version: 3.5
Django Version: 1.11.x
- MY PROBLEM
What Is my Error: django.core.exceptions.FieldError
What are the Details: Invalid field name(s) for model Page: ‘category’.
What does the Error mean?: Per The Docs, This error is raised when there is a problem with a field inside a model..Of the
reasons listed The following look relevant to my issue:
The Traceback
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()
models.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
for what it’s worth, this issue persists even if I rebuild the database. (rm app.db, makemigrations, migrate)
Advertisement
Answer
class Page(models.Model):
Category = models.ForeignKey(Category)
Variable names are case sensitive – this includes field names and other class attributes. Change Category = models.ForeignKey(Category) to category = models.ForeignKey(Category) to fit model coding style then rebuild your db tables and you should be ok to do Page.objects.get_or_create(category=cat...