Tim,
I wanted to offload the UUID generation for the PK to the server (
server_default instead of just default argument). But I wasn’t able to find
gen_random_uuid() <https://www.postgresql.org/docs/14/functions-uuid.html>
documented in the PostgreSQL dialect
<https://docs.sqlalchemy.org/en/14/dialects/postgresql.html>, should
probably be under Column Valued Functions
<https://docs.sqlalchemy.org/en/14/dialects/postgresql.html#column-valued-functions>
?
So I ended up using server_default=text("gen_random_uuid()")
Is that the (currently) recommended way? It seems to work…
Thanks!
Jens
On Thursday, January 4, 2018 at 7:50:21 AM UTC+10 [email protected] wrote:
> Thanks so much! Really appreciate the example.
>
>
>
>
> On Wednesday, January 3, 2018 at 3:46:47 PM UTC-5, Mike Bayer wrote:
>>
>> On Wed, Jan 3, 2018 at 1:18 PM, Tim Chen <[email protected]> wrote:
>> > Let's say I'm using a uuid PK for my models with a ` server_default`
>> set to
>> > `gen_random_uuid()` (in PostgreSQL). Is there a way to ensure the
>> > server_default value? I would like to catch any INSERT or UPDATE
>> statements
>> > that set the PK value and raise an error if possible.
>>
>> Sure, I would use a before_cursor_execute() handler that does this.
>> You can see the parameters and the statement coming in and raise an
>> error if they have column values you don't want to see.
>>
>>
>> http://docs.sqlalchemy.org/en/latest/core/events.html#sqlalchemy.events.ConnectionEvents.before_cursor_execute
>>
>>
>> this is cleanest using some of the internal state of the context so
>> here is a demo:
>>
>> from sqlalchemy import *
>> from sqlalchemy.orm import *
>> from sqlalchemy import event
>> from sqlalchemy.ext.declarative import declarative_base
>>
>> Base = declarative_base()
>>
>>
>> class A(Base):
>> __tablename__ = 'a'
>> id = Column(Integer, primary_key=True)
>> x = Column(Integer)
>>
>> e = create_engine("sqlite://", echo=True)
>>
>>
>> @event.listens_for(e, "before_cursor_execute")
>> def receive_before_cursor_execute(conn, cursor, statement, parameters,
>> context, executemany):
>> if context.isinsert:
>> table = context.compiled.statement.table
>> for col in table.primary_key:
>> if col.key in context.compiled.binds:
>> raise TypeError("no pk allowed!")
>>
>>
>> Base.metadata.create_all(e)
>>
>> s = Session(e)
>> s.add(A(x=5))
>> s.commit() # OK
>>
>> s.add(A(id=2, x=7))
>> s.commit() # not OK
>>
>>
>>
>>
>>
>>
>> >
>> > --
>> > SQLAlchemy -
>> > The Python SQL Toolkit and Object Relational Mapper
>> >
>> > http://www.sqlalchemy.org/
>> >
>> > To post example code, please provide an MCVE: Minimal, Complete, and
>> > Verifiable Example. See http://stackoverflow.com/help/mcve for a full
>> > description.
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>
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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