使用 models.Model, [(models.Model) ---> (BaseModel)] 创建一个模型后如何继承另一个模型

Question

我创建了一个这样的模型。

class BloodDiscard(models.Model):
    timestamp = models.DateTimeField(auto_now_add=True, blank=True)
    created_by = models.ForeignKey(Registration, on_delete=models.SET_NULL, null=True)
    blood_group = models.ForeignKey(BloodGroupMaster, on_delete=models.SET_NULL, null=True)
    blood_cells = models.ForeignKey(BloodCellsMaster, on_delete=models.SET_NULL, null=True)
    quantity = models.FloatField()

但是现在我需要对我的模型应用继承，就像这样。 [(models.Model) ---> (BaseModel)]

class BloodDiscard(BaseModel):
    timestamp = models.DateTimeField(auto_now_add=True, blank=True)
    created_by = models.ForeignKey(Registration, on_delete=models.SET_NULL, null=True)
    blood_group = models.ForeignKey(BloodGroupMaster, on_delete=models.SET_NULL, null=True)
    blood_cells = models.ForeignKey(BloodCellsMaster, on_delete=models.SET_NULL, null=True)
    quantity = models.FloatField()

BaseModel 是我之前创建的另一个模型，但忘记在我当前的模型中继承它。

class BaseModel(models.Model):
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    status_master = models.ForeignKey(StatusMaster,on_delete=models.SET_NULL,default=3,null=True, blank=True)

我在更改（models.Model）--->（BaseModel）后应用了“python manage.py makemigrations”并得到了这个......

(venv) G:\office\medicover\medicover_bloodbank_django>python manage.py makemigrations
You are trying to add the field 'created_at' with 'auto_now_add=True' to blooddiscard without a default; the database needs something to populate existing rows.

 1) Provide a one-off default now (will be set on all existing rows)
 2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
You can accept the default 'timezone.now' by pressing 'Enter' or you can provide another value.
The datetime and django.utils.timezone modules are available, so you can do e.g. timezone.now
Type 'exit' to exit this prompt
[default: timezone.now] >>>
Migrations for 'Form':
  Form\migrations\0018_auto_20220622_2322.py
    - Add field created_at to blooddiscard
    - Add field status_master to blooddiscard
    - Add field updated_at to blooddiscard

但在那之后，当我应用“python manage.py migrate”时。 我收到这个错误。

(venv) G:\office\medicover\medicover_bloodbank_django>python manage.py migrate        
Operations to perform:
  Apply all migrations: Form, Master, User, admin, auth, contenttypes, sessions
Running migrations:
  Applying Form.0018_auto_20220622_2322...Traceback (most recent call last):
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
psycopg2.errors.ForeignKeyViolation: insert or update on table "Form_blooddiscard" violates foreign key constraint "Form_blooddiscard_status_master_id_ffe293fa_fk_Master_st"
DETAIL:  Key (status_master_id)=(3) is not present in table "Master_statusmaster".


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

Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    main()
  File "manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\core\management\__init__.py", line 419, in execute_from_command_line
    utility.execute()
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\core\management\__init__.py", line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\core\management\base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\core\management\base.py", line 398, in execute
    output = self.handle(*args, **options)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\core\management\base.py", line 89, in wrapped
    res = handle_func(*args, **kwargs)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\core\management\commands\migrate.py", line 244, in handle
    post_migrate_state = executor.migrate(
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\migrations\executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\migrations\executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\migrations\executor.py", line 227, in apply_migration
    state = migration.apply(state, schema_editor)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\migrations\migration.py", line 126, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\migrations\operations\fields.py", line 104, in database_forwards
    schema_editor.add_field(
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\backends\base\schema.py", line 522, in add_field
    self.execute(sql, params)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\backends\base\schema.py", line 145, in execute
    cursor.execute(sql, params)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\backends\utils.py", line 98, in execute
    return super().execute(sql, params)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\backends\utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\backends\utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "G:\office\medicover\medicover_bloodbank_django\venv\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
django.db.utils.IntegrityError: insert or update on table "Form_blooddiscard" violates foreign key constraint "Form_blooddiscard_status_master_id_ffe293fa_fk_Master_st"
DETAIL:  Key (status_master_id)=(3) is not present in table "Master_statusmaster".

当做“python manage.py runserver”得到这个......

(venv) G:\office\medicover\medicover_bloodbank_django>python manage.py runserver
Watching for file changes with StatReloader
Performing system checks...

System check identified no issues (0 silenced).

You have 1 unapplied migration(s). Your project may not work properly until you apply the migrations for app(s): Form.
Run 'python manage.py migrate' to apply them.
June 22, 2022 - 23:23:51
Django version 3.2.5, using settings 'App.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CTRL-BREAK.

注意：-在 StatusMaster 表中只有两行 id 为 1 和 2。

Answer 1

这是行不通的，因为BaseModel是一个非抽象模型，因此BaseModel和BloodDiscard共享相同的“主键空间”： BaseModel BloodDiscard键的ForeignKey 。

您可能不希望BaseModel成为非抽象模型，而是抽象模型，因此您可以将BaseModel重写为：

class BaseModel(models.Model):
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    status_master = models.ForeignKey(
        StatusMaster,
        on_delete=models.SET_NULL,
        default=3,
        null=True,
        blank=True
    )

    class Meta:
        abstract = True

删除有问题的迁移文件，制作新的迁移文件，然后迁移。

Answer 2

这是我得到的错误：-

django.db.utils.IntegrityError：在表“Form_blooddiscard”上插入或更新违反了外键约束“Form_blooddiscard_status_master_id_ffe293fa_fk_Master_st”详细信息：表“Master_statusmaster”中不存在键（status_master_id）=（3）。

正如我们所看到的：- 详细信息：表“Master_statusmaster”中不存在键（status_master_id）=（3）。

它告诉我，在 status_master 中，没有值为“3”的“id”（PK）。

但是，在我的基本模型中：-

class BaseModel(models.Model):
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    status_master = 

models.ForeignKey(StatusMaster,on_delete=models.SET_NULL,default=3,null=True, blank=True)

有人提供了不存在的“status_master”默认值“3”。 所以，我只是删除了默认值并解决了。