document sequence + server default

[Former user]

When I supply a primary key a custom Sequence the sequence is created but not attached to the primary key column. Tested only with PostgreSQL and SQLAlchemy 1.0.5

example code

from sqlalchemy import Column,Integer, Sequence
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine

Base = declarative_base()


class TestCustomSeq(Base):
    __tablename__ = 'testseq'
    id = Column(Integer, Sequence('customseq'), primary_key=True)


alchemy_engine = create_engine('postgresql://gijs:gijs@localhost:5433/gijs', echo=True)
Base.metadata.create_all(alchemy_engine)

generated sql:

CREATE SEQUENCE customseq
COMMIT;
CREATE TABLE testseq (
    id INTEGER NOT NULL, 
    PRIMARY KEY (id)
);

[Mike Bayer]

if you'd like to make the Sequence a server default, specify the SQL expression you'd like as server_default:

from sqlalchemy import Column,Integer, Sequence
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine

Base = declarative_base()


seq = Sequence('customseq')

class TestCustomSeq(Base):
    __tablename__ = 'testseq'
    id = Column(Integer, seq, server_default=seq.next_value(), primary_key=True)


alchemy_engine = create_engine('postgresql://scott:tiger@localhost/test', echo=True)
Base.metadata.create_all(alchemy_engine)

im -1 on changing anything here. at most just a documentation update.

[Former user]

sure, I just didn't knew how to get this going but this results in what I want to accomplish! thanks.

[Former user]

btw, if you supply optional=True to sequence it does t work, but the name is ignored. That is why I thought the usage was a bit inconsistent

[Mike Bayer]

• add a subsection on how to use Sequence with server_default, fixes #3453

→ <<cset b861b7537c29>>

[Mike Bayer]

• add a subsection on how to use Sequence with server_default, fixes #3453

(cherry picked from commit b861b7537c29349da00793fc828226a68cded62d)

→ <<cset 981685c7b353>>