[Sqlalchemy-tickets] Issue #4305: Sequence for PostgreSQL are not working as expected (zzzeek/sqlalchemy)

[MaxB <iss...@bi...>]

New issue 4305: Sequence for PostgreSQL are not working as expected
https://bitbucket.org/zzzeek/sqlalchemy/issues/4305/sequence-for-postgresql-are-not-working-as

MaxB:

Hi guys!

I use PostgreSQL. I want to create an auto-increment field started from 1000, increment by 2.

My not working code:


```
#!python
class MyTable(db.Model):
    __tablename__ = 'my_table'
    id_seq = Sequence('my_table_id_seq', start=1000, increment=2)
    id = db.Column(db.Integer, id_seq, server_default=id_seq.next_value(), primary_key=True) 

```

In my autogenerated migration scrip I see this (which will obviously not work, because there is no definition for my_table_id_seq):

```
#!python

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.create_table('my_table',
    sa.Column('id', sa.Integer(), server_default=sa.text("nextval('my_table_id_seq')"), nullable=False),
    sa.PrimaryKeyConstraint('id')
    )
    # ### end Alembic commands ###
```


If I run it, I get expected error:


```
#!python

  File "/Users/maxb/Projects/ANDR3/Andr3Admin/venv/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 507, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) relation "my_table_id_seq" does not exist
 [SQL: "\nCREATE TABLE my_table (\n\tid INTEGER DEFAULT nextval('my_table_id_seq') NOT NULL, \n\tPRIMARY KEY (id)\n)\n\n"] (Background on this error at: http://sqlalche.me/e/f405)
```


So, how do I code it to have expected behaviour?

Thanks in advance!