django.db.utils.IntegrityError：NOT NULL 约束失败：polls_article.reporter_id

Question

我正在关注 Django 的官方documentation 进行多对一关系。

创建一篇新文章，并将其添加到文章集中：

>>> new_article2 = Article.objects.create(headline="Paul's story", pub_date=date(2006, 1, 17))

models.py 包括：

从 django.db 导入模型

class Reporter(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    email = models.EmailField()

    def __str__(self):
        return "%s %s" % (self.first_name, self.last_name)

class Article(models.Model):
    headline = models.CharField(max_length=100)
    pub_date = models.DateField()
    reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)

    def __str__(self):
        return self.headline

    class Meta:
        ordering = ('headline',)

但是当我尝试执行时收到错误消息：django.db.utils.IntegrityError: NOT NULL constraint failed: polls_article.reporter_id

追溯：

    >>> new_article2 = Article.objects.create(headline="Paul's story", pub_date=datetime.date(2006, 1, 17))

Traceback (most recent call last):
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/backends/sqlite3/base.py", line 303, in execute
    return Database.Cursor.execute(self, query, params)
sqlite3.IntegrityError: NOT NULL constraint failed: polls_article.reporter_id

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/query.py", line 417, in create
    obj.save(force_insert=True, using=self.db)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/base.py", line 729, in save
    force_update=force_update, update_fields=update_fields)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/base.py", line 759, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/base.py", line 842, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/base.py", line 880, in _do_insert
    using=using, raw=raw)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/query.py", line 1125, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1285, in execute_sql
    cursor.execute(sql, params)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 100, in execute
    return super().execute(sql, params)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 68, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 77, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/home/student/PycharmProjects/DjangoGetStarted/venv/lib/python3.6/site-packages/django/db/backends/sqlite3/base.py", line 303, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: NOT NULL constraint failed: polls_article.reporter_id

Answer 1

您的模型表明从Reporter 到Article 之间存在一对多关系，即一个Reporter 可以与多个Articles 相关联。此外，由于Article 模型的reporter 字段不可 为空，每个Article 必须 有一个Reporter 关联。也就是说，您必须首先创建一个Reporter（类似于您链接到的文档中的示例）：

>>> r = Reporter(first_name='John', last_name='Smith', email='john@example.com')
>>> r.save()

然后将您的Article 与该关联：

>>> a = Article(id=None, headline="This is a test", pub_date=date(2005, 7, 27), reporter=r)
>>> a.save()

Answer 2

您正在创建Article 实例没有reporter 引用，即FK。因此您必须在创建Article 实例时提供FK 对象或FK 的pk，如下所示，

在[2]中：

reporter = Reporter.objects.create(first_name='Jerin', last_name='Peter George', email='myemail@email.com')

在[3]中：

from datetime import datetime

在[4]中：

Article.objects.create(headline= "Jerin's story", pub_date = datetime.utcnow()<b>,reporter=reporter</b>)

输出[4]：

<Article: Paul's story>

如果您希望将记者对象设置为 Article 模型中的 NULL 引用，您必须在您的模型中通过添加 null=True 来提及它

class Article(models.Model):
headline = models.CharField(max_length=100)
pub_date = models.DateField()
reporter = models.ForeignKey(Reporter,
                             <b>null=True,</b> on_delete=models.CASCADE)

def __str__(self):
    return self.headline</code></pre>

因此，您可以在没有reporter 引用的情况下创建文章对象

new_article2 = Article.objects.create(headline="Paul's story", pub_date=datetime.date(2006, 1, 17))