Switching to the new EngineFacade Link to heading

by Roman Podoliaka

@rpodoliaka irc: rpodolyaka rpodolyaka@mirantis.com

slides: http://podoliaka.org/talks/

The new EngineFacade Link to heading

“old” EngineFacade: thread-safe initialization is left up to users Link to heading

_ENGINE_FACADE = None
_LOCK = threading.Lock()

def _create_facade_lazily():
    global _LOCK, _ENGINE_FACADE
    if _ENGINE_FACADE is None:
        with _LOCK:
            if _ENGINE_FACADE is None:
                _ENGINE_FACADE = db_session.EngineFacade.from_config(CONF)
    return _ENGINE_FACADE

“new” EngineFacade: lazy thread-safe initialization Link to heading

from oslo.db import enginefacade as sql

@sql.reader
def some_api_method(context):
    # work with context.session

@sql.writer
def some_other_api_method(context):
    # work with context.session

“new” EngineFacade: multiple instances of EngineFacade Link to heading

main_context_manager = sql.transaction_context()
api_context_manager = sql.transaction_context()

“new” EngineFacade: project specific configuration Link to heading

context_manager = enginefacade.transaction_context()

context_manager.configure(sqlite_fk=True)
context_manager.append_on_engine_create(set_hook)

“old” EngineFacade: get_session() boilerplate Link to heading

@require_context
@handle_db_data_error
def snapshot_create(context, values):
    values['snapshot_metadata'] = \
    	_metadata_refs(values.get('metadata'),
         models.SnapshotMetadata)
    if not values.get('id'):
        values['id'] = str(uuid.uuid4())

    session = get_session()
    with session.begin():
        snapshot_ref = models.Snapshot()
        snapshot_ref.update(values)
        session.add(snapshot_ref)

        return _snapshot_get(context, values['id'],
                             session=session)

“old” EngineFacade: private DB API functions Link to heading

@require_context
def _snapshot_metadata_get(context, snapshot_id,
                           session=None):
    rows = _snapshot_metadata_get_query(
    	context,snapshot_id, session).all()
    result = {}
    for row in rows:
        result[row['key']] = row['value']

    return result

“new” EngineFacade: session scope is managed declaratively Link to heading

@main_context_manager.writer
def quota_destroy_all_by_project_and_user(context,
                                          project_id,
                                          user_id):
    model_query(context, models.ProjectUserQuota,
                read_deleted="no").\
        filter_by(project_id=project_id).\
        filter_by(user_id=user_id).\
        soft_delete(synchronize_session=False)

What projects are already using the new EngineFacade? Link to heading

Need help? Link to heading

Slides: http://podoliaka.org/talks/

Bugs: https://bugs.launchpad.net/oslo.db

Questions: