On 11/18/2016 11:25 AM, Alexander O'Donovan-Jones wrote:
That's a cool idea, but it would need to reference the instance we've
created to use the `id` atribute.
I was almost going to ask if that's what you meant, but you didn't
specify that in your question. Simon's answer contains the adjustment
you'd need.
ie the sql would be `select max(version)+1 from responses where id = :id`
On Friday, 18 November 2016 14:39:52 UTC, Mike Bayer wrote:
On 11/18/2016 09:10 AM, Alexander O'Donovan-Jones wrote:
> I'm currently working on using the ORM features of sqlalchemy with a
> legacy database table. The table can be roughly described like this:
>
> class APIResponse(Base):
> __tablename__ = 'responses'
> id = Column(Text, primary_key=True)
> version = Column(Integer, primary_key=True)
> payload = Column(JSONB, nullable=False)
> created_at = Column(DateTime, nullable=False)
>
>
> The table stores JSON payloads where the primary key is determined by
> the combination of the id and version columns (as a composite primary
> key). What I'm trying to work out is whether it's possible to have
the
> value of the version column be the result of
> func.max(APIResponse.version) + 1, that is, MAX()+1 to increment the
> version.
>
> This is running on Postgresql, and so I took a look at the sequence
> support, but that appears to be a table wide sequence, and not
keyed off
> a value (ie: I couldn't have 10000 id's each mapping to a sequence to
> generate versions).
you can set any SQL expression you want for a default, some examples at
https://docs.sqlalchemy.org/en/latest/core/defaults.html#sql-expressions
<https://docs.sqlalchemy.org/en/latest/core/defaults.html#sql-expressions>.
This would look like
default=select([func.max(API.response.version) +
1]). hope that helps.
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