Django South 迁移后整个表丢失答案

【问题标题】：Entire table missing after Django South migrationDjango South 迁移后整个表丢失
【发布时间】：2013-07-27 00:26:38
【问题描述】：

在自动生成的 Django South (0.7.6) 迁移文件中，它包含一个简单的前向迁移，该迁移删除了对 field 的唯一约束，然后将该字段作为另一个 Django 模型的外键。

class Migration(SchemaMigration):

    def forwards(self, orm):

        # Removing unique constraint on 'model2', fields ['field']
        db.delete_unique('app2_model2', ['field_id'])

        # Changing field 'model2.field'
        db.alter_column('app2_model2', 'field_id', self.gf('django.db.models.fields.related.ForeignKey')(null=True, to=orm['app1.model1']))

当我在 InnoDB 引擎上运行的 MySQL 5.5 数据库上执行该操作时，它“无法重命名”表

...
File "/opt/python/bundle/3/app/apps/app2/migrations/0020_auto__chg_field_model2_field__del_unique_model2_field__chg_field_model2.py", line 19, in forwards
    db.alter_column('app2_model2', 'field_id', self.gf('django.db.models.fields.related.ForeignKey')(null=True, to=orm['app1.model1']))
File "/opt/python/run/venv/lib/python2.6/site-packages/south/db/generic.py", line 44, in _cache_clear
    return func(self, table, *args, **opts)
File "/opt/python/run/venv/lib/python2.6/site-packages/south/db/generic.py", line 487, in alter_column
    self.delete_foreign_key(table_name, name)
File "/opt/python/run/venv/lib/python2.6/site-packages/south/db/generic.py", line 44, in _cache_clear
    return func(self, table, *args, **opts)
File "/opt/python/run/venv/lib/python2.6/site-packages/south/db/generic.py", line 780, in delete_foreign_key
    "constraint": self.quote_name(constraint_name),
File "/opt/python/run/venv/lib/python2.6/site-packages/south/db/generic.py", line 273, in execute
    cursor.execute(sql, params)
File "/opt/python/run/venv/lib/python2.6/site-packages/django/db/backends/mysql/base.py", line 114, in execute
    return self.cursor.execute(query, args)
File "/opt/python/run/venv/lib/python2.6/site-packages/MySQLdb/cursors.py", line 174, in execute
    self.errorhandler(self, exc, value)
File "/opt/python/run/venv/lib/python2.6/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
django.db.utils.DatabaseError: (1025, "Error on rename of './ebdb/#sql-260e_45b9' to './ebdb/app2_model2' (errno: 150)")

这意味着该表已被有效擦除，并且对 Django 不可见：

...
    cursor.execute(sql, params)
File "/opt/python/run/venv/lib/python2.6/site-packages/django/db/backends/mysql/base.py", line 114, in execute
    return self.cursor.execute(query, args)
File "/opt/python/run/venv/lib/python2.6/site-packages/MySQLdb/cursors.py", line 174, in execute
    self.errorhandler(self, exc, value)
File "/opt/python/run/venv/lib/python2.6/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
DatabaseError: (1146, "Table 'ebdb.app2_model2' doesn't exist")

数据库已恢复并重新运行此迁移，重复了五次，确信此迁移并非偶然失败。

我的问题是：出了什么问题？

【问题讨论】：

标签： mysql innodb django-south database-migration

【解决方案1】：

发现问题。这发生在将唯一、一对一 Django 关系转换为简单外键关系的罕见组合中，使用没有唯一性约束，在 MySQL 表上完成，MyISAM 或 InnoDB，因为MySQL supports transactional schema alterations on neither，即使引擎这样做。

为了解决这个问题，我刚刚删除了the advice of a kind fellow 之后的db.alter_column 命令，他发现OneToOne 关系和ForeignKey 关系之间的底层架构没有功能差异。

【讨论】：