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python - Django 3.0x 中如何以及为什么会出现外键完整性错误？

问题描述

我正在尝试在 Django 中创建一个待办事项列表应用程序，并且我想将用户的个人资料链接到他自己的待办事项列表、待办事项列表项和一个额外的截止日期类。

我目前正在尝试使用 createsuperuser 创建我的超级用户。但是，我收到一个异常，因为我的外键约束失败了。以下是回溯：

File "manage.py", line 21, in <module>
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/core/management/__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/core/management/base.py", line 328, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/contrib/auth/management/commands/createsuperuser.py", line 79, in execute
    return super().execute(*args, **options)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/core/management/base.py", line 369, in execute
    output = self.handle(*args, **options)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/contrib/auth/management/commands/createsuperuser.py", line 189, in handle
    self.UserModel._default_manager.db_manager(database).create_superuser(**user_data)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/contrib/auth/models.py", line 158, in create_superuser
    return self._create_user(username, email, password, **extra_fields)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/contrib/auth/models.py", line 141, in _create_user
    user.save(using=self._db)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/contrib/auth/base_user.py", line 66, in save
    super().save(*args, **kwargs)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/base.py", line 746, in save
    force_update=force_update, update_fields=update_fields)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/base.py", line 795, in save_base
    update_fields=update_fields, raw=raw, using=using,
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/dispatch/dispatcher.py", line 175, in send
    for receiver in self._live_receivers(sender)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/dispatch/dispatcher.py", line 175, in <listcomp>
    for receiver in self._live_receivers(sender)
  File "/Users/ganesh/dev/WebApp/WebApp/users/signals.py", line 10, in create_profile
    Profile.objects.create(user=instance)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/query.py", line 433, in create
    obj.save(force_insert=True, using=self.db)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/base.py", line 746, in save
    force_update=force_update, update_fields=update_fields)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/base.py", line 784, in save_base
    force_update, using, update_fields,
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/base.py", line 886, in _save_table
    results = self._do_insert(cls._base_manager, using, fields, returning_fields, raw)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/base.py", line 925, in _do_insert
    using=using, raw=raw,
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/query.py", line 1204, in _insert
    return query.get_compiler(using=using).execute_sql(returning_fields)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/models/sql/compiler.py", line 1377, in execute_sql
    cursor.execute(sql, params)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/backends/utils.py", line 100, in execute
    return super().execute(sql, params)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/backends/utils.py", line 68, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/backends/utils.py", line 77, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/backends/utils.py", line 86, in _execute
    return self.cursor.execute(sql, params)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/backends/utils.py", line 86, in _execute
    return self.cursor.execute(sql, params)
  File "/Users/ganesh/dev/WebApp/lib/python3.7/site-packages/django/db/backends/sqlite3/base.py", line 396, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: FOREIGN KEY constraint failed

这是我的models.py类：

from django.db import models
from django.contrib.auth.models import User
import os
from django.db.models.signals import post_save
import datetime

class ToDoItem(models.Model):
    item_name = models.CharField(max_length = 150)
    item_type = models.CharField(max_length = 20)
    item_desc = models.TextField()

    class Meta:
        verbose_plural_name = "ToDoItems"

    def __str__(self):
        return self.item_name


class ToDoList(models.Model):
    all_lists = models.TextField()

    item = models.ForeignKey(ToDoItem, default = 1, verbose_name = "ToDoItems",on_delete = models.SET_DEFAULT)

    class Meta:
        verbose_name_plural = "ToDoLists"


    def __str__(self):
        return self.all_lists   

class Deadline(models.Model):
    deadline_heading = models.CharField(max_length = 50)
    deadline_desc = models.TextField()
    deadline_due = models.DateTimeField("Date Due", default =datetime.date.today()+datetime.timedelta(days=7))

    class Meta:
        verbose_name_plural = "Deadlines"

    def __str__(self):
        return self.deadline_heading

class Profile(models.Model):

    user = models.OneToOneField(User, on_delete=models.CASCADE)

    dl = models.ForeignKey(Deadline, default = 1, verbose_name = "Deadlines", on_delete = models.SET_DEFAULT)

    col_list = models.ForeignKey(ToDoList, default = 1, verbose_name = "ToDoLists", on_delete = models.SET_DEFAULT)


    def __str__(self):
        return f'{self.user.username} Profile'

我了解我的代码和数据库之间存在一些差异。但是，我无法准确指出问题所在。有人可以指出我的错误吗？

我也想知道如何克服这个问题，以及将来我能做些什么来避免这样的问题。有什么建议么？

我非常感谢您的帮助。提前非常感谢。

标签： pythondjangopython-3.xdjango-models

解决方案

您的错误发生在这里：

File "/Users/ganesh/dev/WebApp/WebApp/users/signals.py", line 10, in   create_profile
Profile.objects.create(user=instance)

可能是因为 id=1 的 Deadline 或 id=1 的 ToDoList 引用了相关数据库表中不存在的实例。您可以确保在数据库中创建它们。

您还可以从字段定义中删除默认值并添加 null=True：

dl = models.ForeignKey(Deadline, null=True, verbose_name = "Deadlines", on_delete = models.SET_NULL)
col_list = models.ForeignKey(ToDoList, null=True, verbose_name = "ToDoLists", on_delete = models.SET_NULL)

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