def session_reset(ssn: sa.orm.Session):
""" Reset the session when done """
yield
ssn.rollback()
ssn.expunge_all()
def test_does_not_lose_history(ssn: sa.orm.Session):
""" Extensive test of InstanceHistoryProxy with query counters and lazy loads """
assert ssn.autoflush == False, 'this test relies on Session.autoflush=False'
engine = ssn.get_bind()
# Prepare
ssn.add(User(id=1, name='John', age=18))
ssn.add(Article(id=1, title='Python', author_id=1))
ssn.commit()
# === Test 1: ModelHistoryProxy does not lose history when flushing a session
ssn.expunge_all(
) # got to reset; otherwise, the session might reuse loaded objects
user = ssn.query(User).get(1)
with ExpectedQueryCounter(engine, 0, 'Expected no queries here'):
old_user_hist = InstanceHistoryProxy(user) # issues no queries
# Modify
user.name = 'CHANGED'
# History works
assert old_user_hist.name == 'John'
# Flush
ssn.flush()
# History is NOT broken!
assert old_user_hist.name == 'John'
# Change another column after flush; history is still NOT broken!
user.age = 1800
assert old_user_hist.age == 18 # correct
# Undo
ssn.rollback()
# === Test 1: ModelHistoryProxy does not lose history when lazyloading a column
ssn.expunge_all(
) # got to reset; otherwise, the session might reuse loaded objects
user = ssn.query(User).options(load_only('name')).get(1)
with ExpectedQueryCounter(engine, 0, 'Expected no queries here'):
old_user_hist = InstanceHistoryProxy(user) # issues no queries
user.name = 'CHANGED'
assert old_user_hist.name == 'John'
# Load a column
with ExpectedQueryCounter(engine, 1, 'Expected 1 lazyload query'):
user.age # get an unloaded column
# History is NOT broken!
assert old_user_hist.name == 'John'
# === Test 2: ModelHistoryProxy does not lose history when lazyloading a one-to-many relationship
ssn.expunge_all(
) # got to reset; otherwise, the session might reuse loaded objects
user = ssn.query(User).get(1)
with ExpectedQueryCounter(engine, 0, 'Expected no queries here'):
old_user_hist = InstanceHistoryProxy(user)
user.name = 'CHANGED'
assert old_user_hist.name == 'John' # History works
# Load a relationship
with ExpectedQueryCounter(engine, 1, 'Expected 1 lazyload query'):
list(user.articles)
# History is NOT broken!
assert old_user_hist.name == 'John'
# === Test 3: ModelHistoryProxy does not lose history when lazyloading a one-to-one relationship
ssn.expunge_all(
) # got to reset; otherwise, the session might reuse loaded objects
article = ssn.query(Article).get(1)
with ExpectedQueryCounter(engine, 0, 'Expected no queries here'):
old_article_hist = InstanceHistoryProxy(article)
article.title = 'CHANGED'
assert old_article_hist.title == 'Python' # works
# Load a relationship
with ExpectedQueryCounter(engine, 1, 'Expected 1 lazyload query'):
article.author
# History is NOT broken!
assert old_article_hist.title == 'Python' # works