The tables are:
user_t = Table('users', meta,
Column('id', Integer, primary_key=True),
Column('name', String(20), nullable=False),
)
post_t = Table('posts', meta,
Column('id', Integer, primary_key=True),
Column('author_id', Integer, ForeignKey('users.id')),
Column('title', String(200), nullable=False),
Column('body', TEXT, nullable=False),
)
And the mappers are:
user_pcount_view = select(
[c for c in user_t.c]+[func.count(post_t.c.id).label('post_count')],
from_obj = [outerjoin(user_t, post_t)],
group_by = [c for c in user_t.c],
).alias('user_pcount')
mapper(User, user_pcount_view)
mapper(Post, post_t, properties={
'author': relation(User, lazy=False, backref='posts')
})
But I found that User.post_count was always None .
The full code is below:
from sqlalchemy import *
meta = DynamicMetaData()
user_t = Table('users', meta,
Column('id', Integer, primary_key=True),
Column('name', String(20), nullable=False),
)
post_t = Table('posts', meta,
Column('id', Integer, primary_key=True),
Column('author_id', Integer, ForeignKey('users.id')),
Column('title', String(200), nullable=False),
Column('body', TEXT, nullable=False),
)
engine = create_engine('sqlite://') # in memory
meta.connect(engine)
meta.create_all()
class User(object):
def __init__(self, name):
self.name = name
class Post(object):
def __init__(self, title, body):
self.title = title
self.body = body
user_pcount_view = select(
[c for c in user_t.c]+[func.count(post_t.c.id).label('post_count')],
from_obj = [outerjoin(user_t, post_t)],
group_by = [c for c in user_t.c],
).alias('user_pcount')
mapper(User, user_pcount_view)
mapper(Post, post_t, properties={
'author': relation(User, lazy=False, backref='posts')
})
session = create_session(bind_to=engine)
engine.echo = False
session.echo_uow = False
user1 = User('user1')
user1.posts.append(Post('post1', 'post1 content...'))
user1.posts.append(Post('post2', 'post2 content...'))
session.save(user1)
session.flush()
user = session.query(User).selectone_by(name='user1')
assert user.post_count==2, 'user.post_count is %s'%user.post_count
# AssertionError: user.post_count is None
--
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