Django-将ForeignKey关系更改为OneToOne [英] Django - Change a ForeignKey relation to OneToOne

问题描述

我在我的Django应用中使用South.我有两个模型正在从具有ForeignKey关系更改为具有OneToOneField关系.当我在开发数据库上运行此迁移时，它运行良好.当迁移作为创建测试数据库的一部分而运行时，最新的迁移失败，并显示MySQL 1005错误:无法创建表mydb.#sql-3249_1d(errno:121)".进行一些谷歌搜索显示，尝试添加与现有约束同名的约束通常是一个问题.迁移失败的具体行是:

I am using South with my Django app. I have two models that I am changing from having a ForeignKey relation to having a OneToOneField relation. When I ran this migration on my dev database, it ran fine. When the migrations get ran as part of creating a test database, the latest migration fails with a MySQL 1005 error: "Can't create table mydb.#sql-3249_1d (errno: 121)". Doing some Googling revealed that this is usually a problem with trying to add a constraint with the same name as an existing constraint. The specific line in the migration that it fails on is:

关系从以下位置更改:

class MyModel(models.Model):
    othermodel = models.ForeignKey(OtherModel)

到

class MyModel(models.Model):
    othermodel = models.OneToOneField(OtherModel)

在迁移过程中生成了以下语句:

which generated the following statements in the migration:

db.alter_column('myapp_mymodel', 'othermodel_id', self.gf('django.db.models.fields.related.OneToOneField')(to=orm['myapp.OtherModel'], unique=True))

db.create_unique('myapp_mymodel', ['othermodel_id'])

但不是在create_unique调用上失败，而是在alter_column调用上失败.我运行以下命令来查看正在生成的SQL:

But instead of failing on the create_unique call, it is failing on the alter_column call. I ran the following command to see what SQL was being generated:

python manage.py migrate myapp 0010 --db-dry-run --verbosity=2

并打印出

myapp:0010_auto__chg_field_mymodel_othermodel__add_unique_mymodel
   = ALTER TABLE `myapp_mymodel` ADD CONSTRAINT `myapp_mymodel_othermodel_id_uniq` UNIQUE (`othermodel_id`) []
   = SET FOREIGN_KEY_CHECKS=1; []
   = ALTER TABLE `myapp_mymodel` ADD CONSTRAINT `myapp_mymodel_othermodel_id_uniq` UNIQUE (`othermodel_id`) []

它试图两次运行ADD CONSTRAINT似乎很奇怪，但是如果删除db.create_unique调用，用--db-dry-run运行它时不会生成SQL，但是如果运行，我仍然会收到错误消息它是真实的.

It seems strange that it is trying to run the ADD CONSTRAINT twice, but if I remove the db.create_unique call, no SQL is generated when I run it with --db-dry-run, but I still get the error if I run it for real.

我在这里很茫然，不胜感激.

I am at a loss here, any help is appreciated.

推荐答案

您实际上根本不需要迁移.在挂钩下，OneToOne和ForeignKey关系具有兼容的数据库模式:一个简单的列，其中一个表中有另一个对象ID.

You actually don't need a migration at all. OneToOne and ForeignKey relations have a compatible database schema under the hook: a simple column witht the other object ID in one of the table.

如果您不想让告诉南方忽略此更改的麻烦，只需使用migrate --fake伪造迁移内容即可.

Just fake the migration with migrate --fake if you don't want to enter in the trouble of telling south to ignore this change.

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