Djangoにて、管理画面からデータを追加しようとすると外部キー制約エラーが発生する

PythonのフレームワークDjangoの勉強で日記を登録するwebサイトを開発しています。

管理画面(adminページ)からDiaryテーブルへデータを追加/更新/削除をしようとすると[FOREIGN KEY constraint failed]と表示され、正常に処理がされません。
直接[python manage.py shell]からDBにデータを追加/更新/削除を実施したところ、正常に処理が行えましたので、本当に外部キー制約により、問題が発生しているのか、判断がつきません。
解決方法に心当たりがある方がいましたら、考えて頂けないでしょうか。

下記にmodelsファイルを記載します。
mysite>
------>accounts>models.py
------>diary>models.py

accounts.models

python
1from django.contrib.auth.models import AbstractUser
2
3class CustomUser(AbstractUser):
4
5    class Meta:
6        verbose_name_plural = 'CustomUser'
7
8

diary.models

python
1from accounts.models import CustomUser
2from django.db import models
3
4class Diary(models.Model):
5    user = models.ForeignKey(CustomUser,
6                             verbose_name='ユーザー', on_delete=models.PROTECT)
7    title = models.CharField(verbose_name='タイトル', max_length=40)
8    content = models.TextField(verbose_name='本文', blank=True, null=True)
9    photo1 = models.ImageField(verbose_name='写真1', blank=True, null=True)
10    photo2 = models.ImageField(verbose_name='写真2', blank=True, null=True)
11    photo3 = models.ImageField(verbose_name='写真3', blank=True, null=True)
12    created_at = models.DateTimeField(verbose_name='作成日時', auto_now_add=True)
13    updated_at = models.DateTimeField(verbose_name='更新日時', auto_now=True)
14
15    class Meta:
16        verbose_name_plural = 'Diary'
17
18        def __str__(self):
19            return self.title

エラーメッセージ

Environment:


Request Method: POST
Request URL: http://127.0.0.1:8000/admin/diary/diary/3/change/

Django Version: 3.0.10
Python Version: 3.8.6
Installed Applications:
['accounts.apps.AccountsConfig',
 'diary.apps.DiaryConfig',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'django.contrib.sites',
 'allauth',
 'allauth.account',
 'allauth.socialaccount']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']



Traceback (most recent call last):
  File "C:\Users\koki\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\db\backends\base\base.py", line 243, in _commit
    return self.connection.commit()

The above exception (FOREIGN KEY constraint failed) was the direct cause of the following exception:
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\core\handlers\exception.py", line 34, in inner
    response = get_response(request)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\core\handlers\base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\core\handlers\base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\contrib\admin\options.py", line 607, in wrapper
    return self.admin_site.admin_view(view)(*args, **kwargs)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\utils\decorators.py", line 130, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\views\decorators\cache.py", line 44, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\contrib\admin\sites.py", line 231, in inner
    return view(request, *args, **kwargs)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\contrib\admin\options.py", line 1641, in change_view
    return self.changeform_view(request, object_id, form_url, extra_context)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\utils\decorators.py", line 43, in _wrapper
    return bound_method(*args, **kwargs)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\utils\decorators.py", line 130, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\contrib\admin\options.py", line 1522, in changeform_view
    return self._changeform_view(request, object_id, form_url, extra_context)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\db\transaction.py", line 232, in __exit__
    connection.commit()
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\utils\asyncio.py", line 26, in inner
    return func(*args, **kwargs)
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\db\backends\base\base.py", line 267, in commit
    self._commit()
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\db\backends\base\base.py", line 243, in _commit
    return self.connection.commit()
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\db\utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "C:\Users\user\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\django\db\backends\base\base.py", line 243, in _commit
    return self.connection.commit()

Exception Type: IntegrityError at /admin/diary/diary/3/change/
Exception Value: FOREIGN KEY constraint failed