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.
This would look like default=select([func.max(API.response.version) +
1]). hope that helps.
I'm not sure if I've explained myself clearly, but I'm a little stumped
as to how I might achieve this.
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