Django的相同型号的误差范围内引用ManyToManyField中没有报价

https://docs.djangoproject.com/en/1.11/topics/db/examples/many_to_many/Django的相同型号的误差范围内引用ManyToManyField中没有报价

所以，我根据我的代码关闭这个文件和我打了一个错误。

from django.db import models 

class Gift(models.Model): 
    name = models.CharField(
     max_length=120, unique=True, help_text='Enter the gift item name' 
    ) 
    # skipping to the ManyToMany .... 
    genre = models.ManyToManyField(Category) 

class Category(models.Model): 
    # skipping stuff like CATEGORIES ... 
    type = models.IntegerField(
     primary_key = True, choices = CATEGORIES, default = EVENT, 
    ) 
    description = models.CharField(max_length=500, null=True, blank=True)

我收到此错误

Traceback (most recent call last): 
    File "manage.py", line 22, in <module> 
    execute_from_command_line(sys.argv) 
    File "/.../gifting_db/lib/python3.6/site-packages/django/core/management/__init__.py", line 363, in execute_from_command_line 
    utility.execute() 
    File "/.../gifting_db/lib/python3.6/site-packages/django/core/management/__init__.py", line 337, in execute 
    django.setup() 
    File "/.../gifting_db/lib/python3.6/site-packages/django/__init__.py", line 27, in setup 
    apps.populate(settings.INSTALLED_APPS) 
    File "/.../gifting_db/lib/python3.6/site-packages/django/apps/registry.py", line 108, in populate 
    app_config.import_models() 
    File "/.../gifting_db/lib/python3.6/site-packages/django/apps/config.py", line 202, in import_models 
    self.models_module = import_module(models_module_name) 
    File "/.../gifting_db/lib/python3.6/importlib/__init__.py", line 126, in import_module 
    return _bootstrap._gcd_import(name[level:], package, level) 
    File "<frozen importlib._bootstrap>", line 978, in _gcd_import 
    File "<frozen importlib._bootstrap>", line 961, in _find_and_load 
    File "<frozen importlib._bootstrap>", line 950, in _find_and_load_unlocked 
    File "<frozen importlib._bootstrap>", line 655, in _load_unlocked 
    File "<frozen importlib._bootstrap_external>", line 678, in exec_module 
    File "<frozen importlib._bootstrap>", line 205, in _call_with_frames_removed 
    File "/.../gifting_db/gifting/gifts/models.py", line 5, in <module> 
    class Gift(models.Model): 
    File "/.../gifting_db/gifting/gifts/models.py", line 20, in Gift 
    category = models.ManyToManyField(Category) 
NameError: name 'Category' is not defined

但是，如果我添加报价到 '类别' 它的工作原理。任何想法为什么？ django doc示例在“发布”和“文章”之间不使用引用https://docs.djangoproject.com/en/1.11/topics/db/examples/many_to_many/。如果有的话，我猜想我把'Category'放在一个字符串中，而不是对Category对象的引用？

genre = models.ManyToManyField('Category')

来源

2017-07-29 myaddresstoday

您的问题是Category是直到Gift之后定义。如果你想使用它没有引号，你需要将Category放在Gift以上。否则，报价工作正常，并提供相同的功能。

https://docs.djangoproject.com/en/dev/ref/models/fields/#foreignkey

如果你需要创建一个尚未被定义的模型的关系，您可以使用该模型的名称，而不是模型对象本身：

来源

2017-07-29 15:28:22

啊，这就是为什么它的报价工作。真棒谢谢你，我错过了在外键部分。 – myaddresstoday

您需要在Gift之前定义Category或使用引号。

from django.db import models 


class Category(models.Model): 
    # skipping stuff like CATEGORIES ... 
    type = models.IntegerField(
    primary_key = True, choices=CATEGORIES, default=EVENT) 
    description = models.CharField(max_length=500, null=True, blank=True) 


class Gift(models.Model): 
    name = models.CharField(max_length=120, unique=True, help_text='Enter the gift item name' 
    ) 
    # skipping to the ManyToMany .... 
    genre = models.ManyToManyField(Category)

或者use quotes

from django.db import models 


class Gift(models.Model): 
    name = models.CharField(max_length=120, unique=True, help_text='Enter the gift item name' 
    ) 
    # skipping to the ManyToMany .... 
    genre = models.ManyToManyField('Category') 


class Category(models.Model): 
    # skipping stuff like CATEGORIES ... 
    type = models.IntegerField(primary_key=True, choices=CATEGORIES, default=EVENT,) 
    description = models.CharField(max_length=500, null=True, blank=True

来源

2017-07-29 15:49:07

Django的相同型号的误差范围内引用ManyToManyField中没有报价

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