changes to attributes are only significant until the next flush occurs. flushing is described at : https://docs.sqlalchemy.org/en/latest/orm/session_basics.html#flushing. When flush() happens, the changes to your attributes are pushed out to the database, and the history is erased. This is because the system only supports a "current" a "previous" value, it is only designed to suit the purposes of session.flush(), which is to show how the attribute differs from what is known to be in the database (in this sense it's really not "history", it's just, "whats in the DB right now?").
An important aspect to flushing is that the Session automatically flushes before each query. This is called autoflush. if you want to look at things that are affected by the flush occurring, you need to turn it off. the docs above illustrate you can set session.autoflush = False, but there is also a context manager that may be more useful; the above documentation will include the link to this manager in the next ten minutes, however it looks like: with session.no_autoflush: myobject.foo = bar session.query(MyObject).all() inspect(myobject).attrs.foo.history direct docs for no_autoflush: https://docs.sqlalchemy.org/en/latest/orm/session_api.html?highlight=no_autoflush#sqlalchemy.orm.session.Session.no_autoflush On Fri, Feb 8, 2019 at 3:22 PM Jim S <ato.st...@gmail.com> wrote: > > Hi > > Newbie here. I think I have a fundamental misunderstanding of either how > session works or you inspect works. My goal is to track changes to my > object. I wrote up this sample to show what I'm having trouble understanding. > > from sqlalchemy import create_engine, inspect > from sqlalchemy import Column, BigInteger, String, Date, Integer > from sqlalchemy.ext.declarative import declarative_base > from sqlalchemy.orm import sessionmaker > > from dateutil.relativedelta import * > > Base = declarative_base() > > > class SaTest(Base): > __tablename__ = 'sa_test' > > id = Column(BigInteger, primary_key=True) > name = Column(String(50)) > dob = Column(Date) > number_of_children = Column(Integer) > > def __repr__(self): > return self.name > > > engine = > create_engine('mysql://mysqluser:mysqlpassword@servername/databasename') > Base.metadata.bind = engine > > DBSession = sessionmaker(bind=engine) > session = DBSession() > > """ > # run this the first time to create the data > jim = SaTest(name='Jim', dob=parse('1971-02-23'), number_of_children=3) > session.add(jim) > > joe = SaTest(name='Joe', dob=parse('1968-06-09'), number_of_children=5) > session.add(joe) > > session.commit() > """ > > jim = session.query(SaTest).filter_by(id=1).one() > jim.dob = jim.dob + relativedelta(days=+14) > jim.number_of_children = jim.number_of_children + 1 > > #joe = session.query(SaTest).filter_by(id=2).first() <---- if I uncomment > this line, inspect doesn't display the changes in history > > insp = inspect(jim) > > for attr, attr_state in insp.attrs.items(): > if attr_state.history.has_changes(): > print('{}: {}'.format(attr, attr_state.value)) > print('History: {}\n'.format(attr_state.history)) > > > I've built this based on the example at the bottom of page 107 in the > O'Reilly Essential SQLAlchemy book. > > It seems to my that running the second query is somehow invalidating the > inspection of the jim object. I'd really like to understand why, but haven't > been able to find anything to help explain it to me. > > Any help would really be appreciated. > > -Jim > > -- > 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 post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at https://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. -- 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 post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
