当我尝试在本地服务器上进行迁移时，一切正常，但是当我尝试在heroku上进行迁移时，它给了我这个DataError。这是回溯。另外，我还是Django的初学者，所以我无法理解此错误。
Operations to perform:
Apply all migrations: admin, auth, contenttypes, mrpash, sessions
Running migrations:
Applying mrpash.0002_auto_20181108_1931...Traceback (most recent call last):
File "/app/.heroku/python/lib/python3.6/site-
packages/django/db/backends/utils.py", line 85, in _execute
return self.cursor.execute(sql, params) psycopg2.DataError: value too long for type character varying(20)
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "manage.py", line 15, in <module>
execute_from_command_line(sys.argv)
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
utility.execute()
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/__init__.py", line 375, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/base.py", line 316, in run_from_argv
self.execute(*args, **cmd_options)
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/base.py", line 353, in execute
output = self.handle(*args, **options)
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/base.py", line 83, in wrapped
res = handle_func(*args, **kwargs)
File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/commands/migrate.py", line 203, in handle
fake_initial=fake_initial,
File "/app/.heroku/python/lib/python3.6/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 "/app/.heroku/python/lib/python3.6/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 "/app/.heroku/python/lib/python3.6/site-packages/django/db/migrations/executor.py", line 244, in apply_migration
state = migration.apply(state, schema_editor)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/migrations/migration.py", line 124, in apply
operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/migrations/operations/fields.py", line 84, in database_forwards
field,
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/schema.py", line 435, in add_field
self.execute(sql, params)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/base/schema.py", line 133, in execute
cursor.execute(sql, params)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py", line 100, in execute
return super().execute(sql, params)
File "/app/.heroku/python/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 "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py", line 77, in _execute_with_wrappers
return executor(sql, params, many, context)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
return self.cursor.execute(sql, params)
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/utils.py", line 89, in __exit__
raise dj_exc_value.with_traceback(traceback) from exc_value
File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
return self.cursor.execute(sql, params)
django.db.utils.DataError: value too long for type character varying(20)
我不知道是哪个字段导致此错误