我正在使用 Alembic 迁移工具在 SQLAlchemy 迁移中添加新的枚举成员。
SQLAlchemy 使用 Python 原生 Enum
作为:
from enum import Enum
class MyEnum(Enum):
# Key and value names different to clarify they are separate
# concepts in Python
old = "OLD_VALUE"
new1 = "NEW1_VALUE"
new2 = "NEW2_VALUE"
然后:
class MyFantasticModel(Base):
__tablename__ = "fantasy"
enum_column = sa.Column(sa.Enum(MyEnum), nullable=False, index=True)
我知道 PostgreSQL is difficult枚举迁移的情况以及类似的问题都有低质量的答案。但我仍然想以半自动化的方式做到这一点。
使用Python 3.8。
最佳答案
您需要手动声明添加的新枚举值,因为很难检测到(尽管并非不可能,但稍后可能会修改此答案)。下面是一个示例迁移,它反射(reflect)了从 Enum
类返回的 PSQL 键。
还有一个降级功能,但只有在没有使用 Enum
值时才会起作用,并且有些危险。
# revision identifiers, used by Alembic.
from mymodels import MyEnum
revision = ...
down_revision = ....
branch_labels = None
depends_on = None
# By default, SQLAlchemy autogenerates PSQL type
# that is the Enum class name lowercased.
# Because Python enums are created using Python metaclasses,
# you cannot directly read the class name back from the class object (it would return `EnumMeta`).
# You need go through method resolution order table to get the real class instance.
# https://stackoverflow.com/a/54014128/315168
enum_name = MyEnum.mro()[0].__name__.lower()
# PostgreSQL does not have a concept of enum keys and values, only values.
# SQLAlchemy maintains enums in the PostgreSQL by the Python enum key (not value)
# Keys to be added:
enum_keys_to_add = [
MyEnum.new1.name,
MyEnum.new2.name,
]
def upgrade():
for v in enum_keys_to_add:
# Use ALTER TYPE.
# See more information https://www.postgresql.org/docs/9.1/sql-altertype.html
op.execute(f"ALTER TYPE {enum_name} ADD VALUE '{v}'")
# Note that ALTER TYPE is not effective within the same transaction https://medium.com/makimo-tech-blog/upgrading-postgresqls-enum-type-with-sqlalchemy-using-alembic-migration-881af1e30abe
def downgrade():
# https://stackoverflow.com/a/39878233/315168
for v in enum_keys_to_add:
sql = f"""DELETE FROM pg_enum
WHERE enumlabel = '{v}'
AND enumtypid = (
SELECT oid FROM pg_type WHERE typname = '{enum_name}'
)"""
op.execute(sql)
您还可以使用以下 SELECT
手动检查 PSQL 枚举的内容:
select enum_range(null::myenum);
enum_range
-----------------------------------------------------------------------------------------------------
{old,new1,new2}
关于postgresql - 如何以半自动方式在 SQLAlchemy for PostgreSQL 中迁移新的 Python Enum 成员?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/70133546/