SQLAlchemy:如何根据列的后端有条件地选择列的类型 [英] SQLAlchemy: How to conditionally choose type for column by depending on its backend

问题描述

我想使用 HSTORE 如果使用PostgreSQL作为后端，则输入列，或者

I want to use HSTORE type for a column if it uses PostgreSQL as its backend, or PickleType otherwise. The problem is that we cannot determine which backend will be used when schema is being defined (in Python). How can I determine this and conditionally choose the data type when the table actually is created on the backend database?

推荐答案

您可以通过

You can accomplish something like this with TypeEngine.with_variant:

from sqlalchemy.types import PickleType
from sqlalchemy.dialects import postgresql

HybridType = PickleType()

HybridType = HybridType.with_variant(postgresql.HSTORE(), 'postgresql')

这会创建一个新类型HybridType，您可以像使用其他任何类型一样使用它，但要注意的是它将在Postgres上生成一个HSTORE列，并在其他任何地方生成一个PickleType.

This creates a new type, HybridType, which you can use like any other type, with the caveat that it will produce an HSTORE column on Postgres and a PickleType everywhere else.

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