DateTimeField的ArrayField会引发 "django.db.utils.ProgrammingError: cannot cast type timestamp with time zone to timestamp with time zone[]"

Question

我正在用Django构建一个应用程序。

我创建了一个新的（仍然是空的）模型，它有一个DateTimeField的ArrayField，定义如下。

Record_time_values = ArrayField(models.DateTimeField(), blank=False, null=False) 

当我运行

python manage.py makemigrations
python manage.py migrate

我得到

django.db.utils.ProgrammingError: cannot cast type timestamp with time zone to timestamp with time zone[] LINE 1: ...estamp with time zone[] USING "Record_time_values"::timestam ...

我做了一些研究，这是 纫 这最接近我的问题，但我不想深究使用SQL来解决这个问题。

难道就没有一个干净的方法可以通过纯python的Django来解决这个问题吗？

另外，有没有一个好的方法可以在模型里面存储一个DateTimeField的数组，绕过arrayfield？

完成回溯。

(met5) C:\Users\Tommaso\Django rest framework\Udemy Django\aqi_luftdaten>python manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, pm_lookup, sessions
Running migrations:
  Applying pm_lookup.0003_auto_20200602_1142...Traceback (most recent call last):
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
psycopg2.errors.CannotCoerce: cannot cast type timestamp with time zone to timestamp with time zone[]
LINE 1: ...estamp with time zone[] USING "Record_time_values"::timestam...
                                                             ^


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

Traceback (most recent call last):
  File "manage.py", line 21, in <module>
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\core\management\__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\core\management\base.py", line 323, in run_from_argv
    self.execute(*args, **cmd_options)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\core\management\base.py", line 364, in execute
    output = self.handle(*args, **options)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\core\management\base.py", line 83, in wrapped
    res = handle_func(*args, **kwargs)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\core\management\commands\migrate.py", line 234, in handle
    fake_initial=fake_initial,
  File "C:\Applicazioni_Tommaso\Phyton\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 "C:\Applicazioni_Tommaso\Phyton\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 "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\migrations\executor.py", line 245, in apply_migration
    state = migration.apply(state, schema_editor)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\migrations\migration.py", line 124, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\migrations\operations\fields.py", line 249, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\base\schema.py", line 535, in alter_field
    old_db_params, new_db_params, strict)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\postgresql\schema.py", line 124, in _alter_field
    new_db_params, strict,
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\base\schema.py", line 685, in _alter_field
    params,
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\base\schema.py", line 137, in execute
    cursor.execute(sql, params)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\utils.py", line 99, in execute
    return super().execute(sql, params)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\utils.py", line 67, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\utils.py", line 76, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "C:\Applicazioni_Tommaso\Phyton\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: cannot cast type timestamp with time zone to timestamp with time zone[]
LINE 1: ...estamp with time zone[] USING "Record_time_values"::timestam...

Answer 1

好的，重现。当你把一列从普通的DateTimeField改变为数组时，就会发生这种情况。如果你只是将该字段创建为一个带有datetimefield的数组字段，那么问题就不会发生。

由于表仍然是空的，你应该做一些迁移维护，而不是创建字段，然后改变它，而是以正确的方式创建它。这可能涉及到回滚一个或多个迁移，这可能会破坏其他表中的数据。如果这是一个问题，那么你应该在做这件事之前备份这些表。请看 逆转迁移 详见。