def run_migrations_online():
"""Run migrations in 'online' mode.
In this scenario we need to create an Engine
and associate a connection with the context.
"""
# this callback is used to prevent an auto-migration from being generated
# when there are no changes to the schema
# reference: http://alembic.zzzcomputing.com/en/latest/cookbook.html
def process_revision_directives(context, revision, directives):
if getattr(config.cmd_opts, 'autogenerate', False):
script = directives[0]
if script.upgrade_ops.is_empty():
directives[:] = []
logger.info('No changes in schema detected.')
engine = engine_from_config(config.get_section(config.config_ini_section),
prefix='sqlalchemy.',
poolclass=pool.NullPool)
connection = engine.connect()
context.configure(connection=connection,
target_metadata=target_metadata,
process_revision_directives=process_revision_directives,
**current_app.extensions['migrate'].configure_args)
try:
with context.begin_transaction():
context.run_migrations()
finally:
connection.close()
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