sqlalchemy and auto increments with postgresql

Question

I created a table with a primary key and a sequence but via the debug ad later looking at the table design, the sequence isn\'t applied, just created.

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Answer 1

I ran into a similar issue with composite multi-column primary keys. The SERIAL is only implicitly applied to a single column primary key. However, this behaviour can be controlled via the autoincrement argument (defaults to "auto"):

id = Column(Integer, primary_key=True, autoincrement=True)

Answer 2

I realize this is an old thread, but I stumbled on it with the same problem and were unable to find a solution anywhere else.

After some experimenting I was able to solve this with the following code:

TABLE_ID = Sequence('table_id_seq', start=1000)

class Table(Base):
    __tablename__ = 'table'

    id = Column(Integer, TABLE_ID, primary_key=True, server_default=TABLE_ID.next_value())

This way the sequence is created and is used as the default value for column id, with the same behavior as if created implicitly by SQLAlchemy.

Answer 3

You specified an explicit Sequence() object with name. If you were to omit that, then SERIAL would be added to the id primary key specification:

CREATE TABLE tramos (
    id INTEGER SERIAL NOT NULL, 
    nombre VARCHAR, 
    tramo_data VARCHAR, 
    estado BOOLEAN, 
    PRIMARY KEY (id)
)

A DEFAULT is only generated if the column is not a primary key.

When inserting, SQLAlchemy will issue a select nextval(..) as needed to create a next value. See the PostgreSQL documentation for details.