Django 南从 MySQL 到 postgresql

Question

我第一次开始在我的一个应用程序中使用 MySQL，现在我正在考虑从 MySQL 迁移到 PostgreSQL。

我为迁移安装了 South。 当我在 postgres 中设置新数据库时，我成功同步了我的应用程序，并在我最后一次迁移中完全停止。

> project:0056_auto__chg_field_project_project_length
Traceback (most recent call last):
  File "./manage.py", line 11, in <module>
    execute_manager(settings)
  File "/Users/ApPeL/.virtualenvs/fundedbyme.com/lib/python2.7/site-packages/django/core/management/__init__.py", line 438, in execute_manager
    utility.execute()
  File "/Users/ApPeL/.virtualenvs/fundedbyme.com/lib/python2.7/site-packages/django/core/management/__init__.py", line 379, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/ApPeL/.virtualenvs/fundedbyme.com/lib/python2.7/site-packages/django/core/management/base.py", line 191, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/Users/ApPeL/.virtualenvs/fundedbyme.com/lib/python2.7/site-packages/django/core/management/base.py", line 220, in execute
    output = self.handle(*args, **options)
  File "/Library/Python/2.7/site-packages/south/management/commands/migrate.py", line 105, in handle
    ignore_ghosts = ignore_ghosts,
  File "/Library/Python/2.7/site-packages/south/migration/__init__.py", line 191, in migrate_app
    success = migrator.migrate_many(target, workplan, database)
  File "/Library/Python/2.7/site-packages/south/migration/migrators.py", line 221, in migrate_many
    result = migrator.__class__.migrate_many(migrator, target, migrations, database)
  File "/Library/Python/2.7/site-packages/south/migration/migrators.py", line 292, in migrate_many
    result = self.migrate(migration, database)
  File "/Library/Python/2.7/site-packages/south/migration/migrators.py", line 125, in migrate
    result = self.run(migration)
  File "/Library/Python/2.7/site-packages/south/migration/migrators.py", line 99, in run
    return self.run_migration(migration)
  File "/Library/Python/2.7/site-packages/south/migration/migrators.py", line 81, in run_migration
    migration_function()
  File "/Library/Python/2.7/site-packages/south/migration/migrators.py", line 57, in <lambda>
    return (lambda: direction(orm))
  File "/Users/ApPeL/Sites/Django/fundedbyme/project/migrations/0056_auto__chg_field_project_project_length.py", line 12, in forwards
    db.alter_column('project_project', 'project_length', self.gf('django.db.models.fields.IntegerField')())
  File "/Library/Python/2.7/site-packages/south/db/generic.py", line 382, in alter_column
    flatten(values),
  File "/Library/Python/2.7/site-packages/south/db/generic.py", line 150, in execute
    cursor.execute(sql, params)
  File "/Users/ApPeL/.virtualenvs/fundedbyme.com/lib/python2.7/site-packages/django/db/backends/postgresql_psycopg2/base.py", line 44, in execute
    return self.cursor.execute(query, args)
django.db.utils.DatabaseError: column "project_length" cannot be cast to type integer

我想知道是否有一些解决方法？

Answer 1

您当前的迁移以这种方式工作：

1. 将列“project_length”更改为另一种类型。

因为你正在做 PostgreSQL 不支持的 alter，所以它坏了。

您必须修复迁移。您可以将其更改为以下迁移（它会起作用，但可能更容易完成）：

1. 使用您希望 project_length 具有的类型和一些默认值创建另一个列 project_length_tmp。
2. 将数据从列 project_length 迁移到 project_lenght_tmp（请参阅南文档中的数据迁移）。
3. 删除列 project_length。
4. 将列 project_length_tmp 重命名为 project_length。

有点复杂的迁移，但它有两个主要优势： 1. 它适用于所有数据库。 2.它与您的旧迁移兼容，因此您只需覆盖旧迁移（更改文件）就可以了。

方法 2

解决您的问题的另一种方法是删除所有迁移并从头开始。如果您的项目只有单一部署，那么它对您来说可以正常工作。

Answer 2

您没有提供正在执行的 SQL 的任何详细信息，但它似乎不太可能是 ALTER TYPE 失败 - 假设 SQL 是正确的。

=> CREATE TABLE t (c_text text, c_date date, c_datearray date[]);
CREATE TABLE
=> INSERT INTO t VALUES ('abc','2011-01-02',ARRAY['2011-01-02'::date,'2011-02-03'::date]);
INSERT 0 1
=> ALTER TABLE t ALTER COLUMN c_text TYPE integer USING (length(c_text));
ALTER TABLE
=> ALTER TABLE t ALTER COLUMN c_date TYPE integer USING (c_date - '2001-01-01');
ALTER TABLE
=> ALTER TABLE t ALTER COLUMN c_datearray TYPE integer USING (array_upper(c_datearray, 1));
ALTER TABLE
=> SELECT * FROM t;
 c_text | c_date | c_datearray 
--------+--------+-------------
      3 |   3653 |           2
(1 row)

没有什么你不能做的。我猜你正在使用的这个 Django 模块生成的 SQL 不正确。