def second_flow(print_function):
session = create_session()
print_function("Reading account 1...")
account = session.query(Account).filter(Account.name == "account1").one()
print_function("Account 1 was read")
print_function("Updating account 1...")
account.amount += Decimal('100')
print_function("Committing...")
session.commit()
print_function("Committed!")
def second_flow(print_function):
transaction_level = "READ COMMITTED"
print_function(
f"Using '{transaction_level}'. We should NOT see uncommitted data...")
session = create_session(transaction_level)
account_count = session.query(Account).count()
print_function(f"Account count: {account_count}")
if account_count == 3:
print_function('Sending email to CEO to say that we got 3 accounts!!!')
def first_flow(print_function):
session = create_session("SERIALIZABLE")
print_function("Reading account 1...")
account = session.query(Account).filter(Account.name == "account1").one()
print_function("Account 1 was read")
print_function('Sleeping...')
sleep(3)
print_function('Waking up...')
account.amount += Decimal('100')
session.commit()
def first_flow(print_function):
session = create_session()
print_function('Adding account 3...')
account3 = Account(name='account3', amount=Decimal('33.33'))
session.add(account3)
print_function('Flushing changes to the DB...')
session.flush()
print_function('Sleeping...')
sleep(5)
print_function('Waking up...')
print_function('We didn\'t commit anything...')
def first_flow(print_function):
session = create_session()
print_function('Adding account 3...')
account3 = Account(name='account3', amount=Decimal('33.33'))
session.add(account3)
print_function('Flushing changes to the DB...')
session.flush()
print_function('Sleeping...')
sleep(5)
print_function('Waking up...')
print_function('Rolling back...')
session.rollback()
print_function('Rolled back!!')
def first_flow(print_function):
transaction_level = "REPEATABLE READ"
session = create_session(transaction_level)
print_function(f"Using '{transaction_level}'. When we read the data first time ")
print_function("we will create a fixed snapshot of the database")
print_database(print_function, session)
print_function('Sleeping...')
sleep(5)
print_function('Waking up...')
print_function("The data in the DB has changed. But if we query it again ")
print_function("we wont see any updates as we will be reading from the transaction snapshot")
print_database(print_function, session)
def first_flow(print_function):
session = create_session()
print_function("Reading account 1...")
account = session.query(Account).filter(
Account.name == "account1").with_for_update().one()
print_function("Account 1 was read")
print_function("Updating account 1...")
account.amount += Decimal('100')
print_function('Sleeping...')
sleep(5)
print_function('Waking up...')
print_function("Committing...")
session.commit()
print_function("Committed!")
def second_flow(print_function):
transaction_level = "READ UNCOMMITTED"
print_function(
f"Using '{transaction_level}'. We should not be surprised to see uncommitted data..."
)
session = create_session(transaction_level)
account_3 = session.query(Account).filter(
Account.name == 'account3').one_or_none()
if account_3:
print_function(
"Updating the newly created account that is not committed yet...")
account_3.amount += 50
print_function('Committing...')
session.commit()
print_function('Committed!!')
def second_flow(print_function):
session = create_session()
print_function('Adding new account at the meantime...')
account3 = Account(name='account3', amount=Decimal('33.33'))
session.add(account3)
account1 = session.query(Account).filter(Account.name == 'account1').one_or_none()
account2 = session.query(Account).filter(Account.name == 'account2').one_or_none()
if account1:
print_function('Updating existing account at the meantime...')
account1.name = 'Updated from second flow'
session.commit()
if account2:
print_function('Deleting existing account at the meantime...')
session.delete(account2)
session.commit()
print_function('Committed!!')
