Hi Simon, Thank you very much. And this also explains why the problem appeared in tests.
Best regards, João On Mon, 14 Dec 2020 at 14:51, Simon King <si...@simonking.org.uk> wrote: > You have missed something important, but I don't know if it will clear > up all your questions :-) > > In your example, c.company_id doesn't get populated until the first > flush. Until then, c.company_id is None. So when you wrote: > > # Case 1: update the _id doesn't seem to reflect > p.company_id = c.company_id > > You were actually writing: > > p.company_id = None > > This explains why p.company and p.company_id are None all the way > through Case 1. > > However, even if you added a session.flush() after adding the objects > to the session, setting a foreign key attribute directly does not > cause the associated relationship to be updated immediately: > > > https://docs.sqlalchemy.org/en/13/faq/sessions.html#i-set-the-foo-id-attribute-on-my-instance-to-7-but-the-foo-attribute-is-still-none-shouldn-t-it-have-loaded-foo-with-id-7 > > Hope that helps, > > Simon > > On Mon, Dec 14, 2020 at 12:50 PM João Miguel Neves > <joao.silva.ne...@gmail.com> wrote: > > > > Hi all, > > > > I'm sorry, as I feel like this is kind of a beginner question. I'd > expect that when I set a column attribute the respective relationship field > would change or at least be marked as changed (so a posterior access can be > loaded later on another access), but I've found a case where it doesn't. > I've tried to find a bit of code to represent what I'm struggling with, > hopefully it will be clear enough. > > > > # --- START --- > > from sqlalchemy import Column, create_engine, ForeignKey, Integer, String > > > > from sqlalchemy.orm import sessionmaker, relationship > > from sqlalchemy.ext.declarative import declarative_base > > > > > > engine = create_engine("sqlite://", echo=True) > > Session = sessionmaker(engine) > > > > Base = declarative_base() > > > > > > class Company(Base): > > __tablename__ = "company" > > > > company_id = Column(Integer, primary_key=True) > > name = Column(String(50)) > > > > > > class Project(Base): > > __tablename__ = "project" > > > > project_id = Column(Integer, primary_key=True) > > name = Column(String(50)) > > company_id = Column(Integer, ForeignKey("company.company_id"), > index=True) > > company = relationship("Company") > > > > > > Base.metadata.create_all(engine) > > > > session = Session() > > > > c = Company(name="First Company") > > > > p = Project(name="First Project") > > > > session.add(c) > > session.add(p) > > > > assert p.company is None > > assert p.company_id is None > > > > # Case 1: update the _id doesn't seem to reflect > > p.company_id = c.company_id > > > > assert p.company is None > > assert p.company_id == c.company_id > > > > session.flush() > > > > # Wasn't expecting the None here > > assert p.company is None > > assert p.company_id is None > > > > session.refresh(p) > > > > # Wasn't expecting the None here > > assert p.company is None > > assert p.company_id is None > > > > # Case 2: update the relation works as expected > > p.company = c > > > > assert p.company == c > > assert p.company_id is None > > > > session.flush() > > > > assert p.company == c > > assert p.company_id == c.company_id > > > > session.refresh(p) > > > > assert p.company == c > > assert p.company_id == c.company_id > > # --- END --- > > > > Sorry for bothering, but I'm really puzzled/stuck and feel like I've > missed something important, > > João > > > > -- > > 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. 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