Hi,
i'm playing with outerjoin defined in the mapper. I'm getting results
different from what I expected, so that I would like to understand which is
the underline logic.
Where a Query w/ outerjoin SELECT has in the backend n rows and would have m
rows in a simple join, I only get m rows plus one 'None' for all the others.
I would have thought to get one instance for each output of the query, am I
wrong?
tanks in advance
sandro
*:-)
The example:
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Table, Column, ForeignKey, text, func
from sqlalchemy.types import *
from sqlalchemy.orm import relation, sessionmaker, mapper, column_property
from sqlalchemy.orm.interfaces import SessionExtension
from datetime import datetime, timedelta
Base = declarative_base()
Base.metadata.bind = 'sqlite://'
Session = sessionmaker(bind=Base.metadata.bind)
sess = Session()
class Entry(Base):
__tablename__ = 'calendar_entry' # Todo and Events
id = Column(Integer, primary_key=True)
summary = Column(String(100))
dtstart = Column(DateTime(timezone=False), nullable=False, index=True)
class Alarm(Base):
__tablename__ = 'calendar_alarm'
ida = Column(Integer, primary_key=True)
trigger = Column(Interval, nullable=False)
# o2m
entry_id = Column(ForeignKey(Entry.id), nullable=False)
entry = relation(Entry, backref='alarm', lazy=True)
Base.metadata.create_all()
e1 = Entry(summary="sum1", dtstart=datetime.now())
e2 = Entry(summary="sum2", dtstart=datetime.now())
a = Alarm(trigger=timedelta(days=1))
ea1 = Entry(summary="entry w/ alarm", dtstart=datetime.now(),alarm=[a])
for e in (e1, e2, ea1, a):
sess.add(e)
sess.commit()
entry_table = Entry.__table__
alarm_table = Alarm.__table__
class MyJoin(object):
def __str__(self):
return "%s" % self.dtstart
m = mapper(MyJoin, entry_table.outerjoin(alarm_table), )
q = sess.query(m)
print q.count()
for r in q.all():
print r
------------------- with result --------------
3 # count for the matches
None ???
2009-04-19 20:34:04.188442 # the only joined entry (entry w/ alarm)
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