I've just done something like this the other day, but it was with an
existing sequence. We're using Alembic for schema updates, so I'm not sure
whether SQLAlchemy's built-in create_all would behave the same way. You
should still be able to use a similar approach.
shared_sequence = Sequence('shared_id__seq')
class ModelA(Base):
shared_id = Column(Integer,
primary_key=True,
default=shared_sequence.next_value(),
server_default=shared_sequence.next_value())
class ModelB(Base):
shared_id = Column(Integer,
primary_key=True,
default=shared_sequence.next_value(),
server_default=shared_sequence.next_value())
This seems to be working fine.
Before that I'd tried providing Sequence as an arg to Column like you have
and I'd run into some problems and this seemed like an easier option.
On Wed, 5 Aug 2020 at 13:59, Zsolt Ero <zsolt....@gmail.com> wrote:
> Hi,
>
> I've split a table into two tables, for performance reasons. I'd like to
> insert into both tables using the same sequence. I'm inserting using
> executemany_mode='values'.
>
> My idea is to call nextval() on the sequence before insert and fill in the
> values client side, before inserting.
>
> select nextval('mysql') FROM generate_series(1,...)
>
> Everything looks good, except for the default behaviour of SQLAlchemy to
> turn an integer + pk column into a SERIAL.
>
> As an alternative I'm also looking at using Sequence('myseq') from
> https://docs.sqlalchemy.org/en/13/dialects/postgresql.html#sequences-serial-identity,
> but this is broken for issuing "CREATE SEQUENCE myseq" before the table
> creation, which is missing the IF NOT EXISTS part.
>
> How can I either:
> - turn off the automatic behaviour of making a pg + int = serial?
> - add a IF NOT EXISTS to the Sequence()?
>
> Or any alternative ideas?
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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