[Sqlalchemy-tickets] Issue #3951: PostgreSQL Sequence not created by metadata.create_all() from declarative mixin (zzzeek/sqlalchemy)

[Andrew P. R. <iss...@bi...>]

New issue 3951: PostgreSQL Sequence not created by metadata.create_all() from declarative mixin
https://bitbucket.org/zzzeek/sqlalchemy/issues/3951/postgresql-sequence-not-created-by

Andrew Paulo Robillo:

I'd been copying this [snippet](https://bitbucket.org/snippets/shimofuri/bALAz) from my old cookbook to add a surrogate key to a declarative table class:


```
#!python

class MixinIntKey(object):
    @declared_attr
    def key(cls):
        return Column(
            pg.INTEGER,
            Sequence(f"sqk_{cls.__tablename__}", 1, 1),
            nullable=False,
            primary_key=True
            )
```
This code was working before (some 3-4 years ago, I think around version 0.8 ): it generates the Sequence when I build the database objects through metadata.create_all(). The only change I made to the snippet was to update it to use format strings (Python 3.6).

After some googling around and testing (see attached file/[link](https://bitbucket.org/snippets/shimofuri/bALAz)), the Sequence can be generated only if the metadata is passed during Sequence init:

```
#!python
Sequence(f"sqk_{cls.__tablename__}", 1, 1, metadata=metadata)
```

My environment: psycopg2==2.7.1, SQLAlchemy==1.1.8, Python 3.6 64bit on Windows 8.1 64bit, PostgreSQL 9.6 server