使用Alembic更改枚举字段 [英] Altering an Enum field using Alembic

问题描述

在使用9.1之前的PostgreSQL版本（为枚举添加ALTER TYPE）时，如何在Alembic迁移中向Enum字段添加元素？ 这个 SO问题解释了直接过程，但我不确定如何做到最好

How can I add an element to an Enum field in an alembic migration when using a version of PostgreSQL older than 9.1 (which adds the ALTER TYPE for enums)? This SO question explains the direct process, but I'm not quite sure how best to translate that using alembic.

这就是我所拥有的：

new_type = sa.Enum('nonexistent_executable', 'output_limit_exceeded',
                   'signal', 'success', 'timed_out', name='status')
old_type = sa.Enum('nonexistent_executable', 'signal', 'success', 'timed_out',
                   name='status')
tcr = sa.sql.table('testcaseresult',
                   sa.Column('status', new_type, nullable=False))


def upgrade():
    op.alter_column('testcaseresult', u'status', type_=new_type,
                    existing_type=old_type)


def downgrade():
    op.execute(tcr.update().where(tcr.c.status==u'output_limit_exceeded')
               .values(status='timed_out'))
    op.alter_column('testcaseresult', u'status', type_=old_type,
                    existing_type=new_type)

以上不幸的是，升级后只能生成 ALTER TABLE测试用例结果ALTER COLUMN状态TYPE状态，实际上什么也没做。

The above unfortunately only produces ALTER TABLE testcaseresult ALTER COLUMN status TYPE status upon upgrade, which essentially does nothing.

推荐答案

我决定尝试直接采用 postgres方法

from alembic import op
import sqlalchemy as sa

old_options = ('nonexistent_executable', 'signal', 'success', 'timed_out')
new_options = sorted(old_options + ('output_limit_exceeded',))

old_type = sa.Enum(*old_options, name='status')
new_type = sa.Enum(*new_options, name='status')
tmp_type = sa.Enum(*new_options, name='_status')

tcr = sa.sql.table('testcaseresult',
                   sa.Column('status', new_type, nullable=False))


def upgrade():
    # Create a tempoary "_status" type, convert and drop the "old" type
    tmp_type.create(op.get_bind(), checkfirst=False)
    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE _status'
               ' USING status::text::_status')
    old_type.drop(op.get_bind(), checkfirst=False)
    # Create and convert to the "new" status type
    new_type.create(op.get_bind(), checkfirst=False)
    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE status'
               ' USING status::text::status')
    tmp_type.drop(op.get_bind(), checkfirst=False)


def downgrade():
    # Convert 'output_limit_exceeded' status into 'timed_out'
    op.execute(tcr.update().where(tcr.c.status==u'output_limit_exceeded')
               .values(status='timed_out'))
    # Create a tempoary "_status" type, convert and drop the "new" type
    tmp_type.create(op.get_bind(), checkfirst=False)
    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE _status'
               ' USING status::text::_status')
    new_type.drop(op.get_bind(), checkfirst=False)
    # Create and convert to the "old" status type
    old_type.create(op.get_bind(), checkfirst=False)
    op.execute('ALTER TABLE testcaseresult ALTER COLUMN status TYPE status'
               ' USING status::text::status')
    tmp_type.drop(op.get_bind(), checkfirst=False)

看来Alembic对 USING <没有直接支持/ code>语句中的 alter_table 方法。

It appears that alembic has no direct support for the USING statement in its alter_table method.

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