[Sqlalchemy-tickets] Issue #4318: Support retrieving Query objects for Bakedqueris (zzzeek/sqlalchemy)

[Sai S. M. <iss...@bi...>]

New issue 4318: Support retrieving Query objects for Bakedqueris
https://bitbucket.org/zzzeek/sqlalchemy/issues/4318/support-retrieving-query-objects-for

Sai Sindhur Malleni:

Trying to use baked queries and refactored this function

def get_oldest_pending_db_row_with_lock(context):
    journal_dep = aliased(models.OpenDaylightJournal)
    dep_query = context.session.query(journal_dep).filter(
        models.OpenDaylightJournal.seqnum == journal_dep.seqnum
    ).outerjoin(
        journal_dep.depending_on, aliased=True).filter(
        or_(models.OpenDaylightJournal.state == odl_const.PENDING,
            models.OpenDaylightJournal.state == odl_const.PROCESSING))
    row = context.session.query(models.OpenDaylightJournal).filter(
        models.OpenDaylightJournal.state == odl_const.PENDING,
        ~ dep_query.exists()
    ).order_by(
        asc(models.OpenDaylightJournal.last_retried)).first()
    if row:
        update_db_row_state(context, row, odl_const.PROCESSING)

    return row

to use baked queries,  as follows:

def get_oldest_pending_db_row_with_lock():
    s = session
    journal_dep = aliased(models.OpenDaylightJournal)
    dep_query = bakery(lambda s1: session.query(journal_dep))
    dep_query += lambda dep_query: dep_query.filter(
        models.OpenDaylightJournal.seqnum == journal_dep.seqnum)
    dep_query += lambda dep_query: dep_query.outerjoin(
        journal_dep.depending_on, aliased=True)
    dep_query += lambda dep_query: dep_query.filter(
        or_(models.OpenDaylightJournal.state == odl_const.PENDING,
            models.OpenDaylightJournal.state == odl_const.PROCESSING))

    row = bakery(lambda s2: session.query(models.OpenDaylightJournal))
    row += lambda row: row.filter(
        models.OpenDaylightJournal.state == odl_const.PENDING,
        ~ dep_query.exists())
    row += lambda row: row.order_by(
        asc(models.OpenDaylightJournal.last_retried))
    row(s).all()
    if row:
        update_db_row_state(row, odl_const.PROCESSING)

    return row

We are seeing a traceback as follows,
Traceback (most recent call last):
  File "saidb.py", line 129, in <module>
    get_oldest_pending_db_row_with_lock_baked()
  File "saidb.py", line 122, in get_oldest_pending_db_row_with_lock_baked
    row(s).all()
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/ext/baked.py", line 434, in all
    return list(self)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/ext/baked.py", line 326, in __iter__
    baked_context = bq._bake(self.session)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/ext/baked.py", line 198, in _bake
    query = self._as_query(session)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/ext/baked.py", line 221, in _as_query
    query = step(query)
  File "saidb.py", line 119, in <lambda>
    ~ dep_query.exists())
AttributeError: 'BakedQuery' object has no attribute 'exists'

So, looks like the query object is not retrievable. Any workarounds, plans to implement this?