[英]How to handle exceptions in a Django migration?
如何在 Django 遷移中捕獲異常?
我有一個遷移,由於各種遺留原因,我預計有時會失敗。 在這種情況下,我希望能夠捕獲該錯誤並運行一些錯誤處理代碼。
具體來說,我正在重命名一個表,有時目標表已經存在,我想合並舊表和新表的內容,然后刪除舊表。
我正在運行 Django 1.7 (:(),我們正計划升級到 1.8,但還沒有發生。
我的遷移是:
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import models, migrations
class Migration(migrations.Migration):
dependencies = [
('main', '0007_migration_name'),
]
operations = [
migrations.AlterModelTable(
name='table_name',
table='LegacyTableName',
),
]
當我運行這個時,我得到
Traceback (most recent call last):
File "manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File ".../django/core/management/__init__.py", line 385, in execute_from_command_line
utility.execute()
File ".../django/core/management/__init__.py", line 377, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File ".../django/core/management/base.py", line 288, in run_from_argv
self.execute(*args, **options.__dict__)
File ".../django/core/management/base.py", line 338, in execute
output = self.handle(*args, **options)
File ".../django/core/management/commands/migrate.py", line 161, in handle
executor.migrate(targets, plan, fake=options.get("fake", False))
File ".../django/db/migrations/executor.py", line 68, in migrate
self.apply_migration(migration, fake=fake)
File ".../django/db/migrations/executor.py", line 102, in apply_migration
migration.apply(project_state, schema_editor)
File ".../django/db/migrations/migration.py", line 108, in apply
operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
File ".../django/db/migrations/operations/models.py", line 236, in database_forwards
new_model._meta.db_table,
File ".../django/db/backends/schema.py", line 350, in alter_db_table
"new_table": self.quote_name(new_db_table),
File ".../django/db/backends/schema.py", line 111, in execute
cursor.execute(sql, params)
File ".../django/db/backends/utils.py", line 81, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
File ".../django/db/backends/utils.py", line 65, in execute
return self.cursor.execute(sql, params)
File ".../django/db/utils.py", line 94, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File ".../django/db/backends/utils.py", line 65, in execute
return self.cursor.execute(sql, params)
File ".../django/db/backends/mysql/base.py", line 129, in execute
return self.cursor.execute(query, args)
File ".../MySQLdb/cursors.py", line 226, in execute
self.errorhandler(self, exc, value)
File ".../MySQLdb/connections.py", line 36, in defaulterrorhandler
raise errorvalue
django.db.utils.OperationalError: (1050, "Table 'LegacyTableName' already exists")
遷移本身提供的只是operations
列表, 文檔中似乎沒有可選的錯誤處理參數。
如何捕獲 OperationalError 以便我可以運行一些 Python 來合並表?
嘗試在 Python 中捕獲數據庫異常的問題在於它們可能不夠具體——例如, OperationalError
可能由於各種原因而出現(其中只有一個是表名已更改)。
我建議您不要嘗試捕獲異常,而是編寫自己的遷移函數來執行任何必要的檢查/修改。 請參閱有關RunPython
的文檔。
這通常是您用於創建數據遷移、運行自定義數據更新和更改以及您需要訪問 ORM 和/或 Python 代碼的任何其他操作的操作。
在您的情況下,您將編寫一個函數來檢查表是否存在並針對任一情況執行一些操作。
編寫這些函數時需要注意一些特定於數據庫的問題,例如:
例如,在 PostgreSQL 上,您應該避免在同一遷移中組合模式更改和 RunPython 操作,否則您可能會遇到錯誤。
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