Dear Mike and SQLAlchemy users, I think I've discovered a confusing (and undocumented) limitation of the refresh_flush event. It's called when non-PK columns are populated after an INSERT or UPDATE (e.g. from a server-side default), but not for PK values.
The documentation<https://docs.sqlalchemy.org/en/13/orm/events.html#sqlalchemy.orm.events.InstanceEvents.refresh_flush> says: "This event is the same as InstanceEvents.refresh()<https://docs.sqlalchemy.org/en/13/orm/events.html#sqlalchemy.orm.events.InstanceEvents.refresh> except it is invoked within the unit of work flush process, and the values here typically come from the process of handling an INSERT or UPDATE, such as via the RETURNING clause or from Python-side default values." With Postgres and SQLite at least, the primary key (e.g. the ID column) of a newly created object is returned with a RETURNING clause. But it doesn't trigger a refresh_flush event, because it's skipped by this code in _postfetch: if returning_cols: row = result.context.returned_defaults if row is not None: for col in returning_cols: # pk cols returned from insert are handled # distinctly, don't step on the values here if col.primary_key and result.context.isinsert: continue I can see that the ID is assigned to the object's state in the caller (_emit_insert_statements): primary_key = result.context.inserted_primary_key if primary_key is not None: # set primary key attributes for pk, col in zip( primary_key, mapper._pks_by_table[table] ): prop = mapper_rec._columntoproperty[col] if state_dict.get(prop.key) is None: state_dict[prop.key] = pk But no event is called when this happens (AFAICS). The after_flush and after_flush_postexec events are called soon after that. It would be nice if at least the documentation made this clear, and even better if we could use refresh_flush for all flush-context events, including PK assignment. What do you think? If an example is useful, here is a trivial one. The receive_refresh_flush handler is never called: from sqlalchemy import Column, Integer, Text, create_engine, event from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker Base = declarative_base() class Dog(Base): __tablename__ = 'dog' id = Column(Integer, primary_key=True) name = Column(Text) engine = create_engine('sqlite://') # engine.echo = True Base.metadata.create_all(engine) DBSession = sessionmaker(bind=engine) session = DBSession(autocommit=True) @event.listens_for(Dog, 'refresh_flush') def receive_refresh_flush(target, flush_context, attrs): print("Dog was assigned an ID: {attrs}") with session.begin() as trans: session.add(Dog(name="fido")) Thanks, Chris. This email is confidential. If you are not the intended recipient, please advise us immediately and delete this message. The registered name of Cantab- part of GAM Systematic is Cantab Capital Partners LLP. See - http://www.gam.com/en/Legal/Email+disclosures+EU for further information on confidentiality, the risks of non-secure electronic communication, and certain disclosures which we are required to make in accordance with applicable legislation and regulations. If you cannot access this link, please notify us by reply message and we will send the contents to you. GAM Holding AG and its subsidiaries (Cantab – GAM Systematic) will collect and use information about you in the course of your interactions with us. Full details about the data types we collect and what we use this for and your related rights is set out in our online privacy policy at https://www.gam.com/en/legal/privacy-policy. Please familiarise yourself with this policy and check it from time to time for updates as it supplements this notice. -- 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. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sqlalchemy/BCCA73C2165E8947A2E786EC482564DE0167FDC820%40CCPMAILDAG03.cantab.local.
