在SQLAlchemy中使用sum（）和unnest（）

Question

I'm trying to figure out proper syntax for using sum and unnest , but I have yet to figure out the proper syntax as currently generated SQL is invalid for PostgreSQL:

sqlalchemy.exc.ProgrammingError: (ProgrammingError) could not determine polymorphic type because input has type "unknown"
 'SELECT (SELECT sum(foo) AS sum_1 \nFROM unnest(%(unnest_1)s) AS foo) AS anon_1 \nFROM products' {'unnest_1': 'stock'}

Working SQL would be:

SELECT (SELECT sum(foo) AS sum_1 FROM unnest(stock) AS foo) AS anon_1 FROM products;

Example test script is here:

from sqlalchemy import Column, Integer, select
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.dialects.postgresql import ARRAY

from sqlalchemy import func as F
from sqlalchemy.sql import column

import logging

Base = declarative_base()

db = create_engine('postgresql://scott:tiger@localhost/')

# create a configured "Session" class
Session = sessionmaker(bind=db)
session = Session()

logging.basicConfig()

class P(Base):
    __tablename__ = 'products'

    id = Column(Integer, primary_key=True)
    stock = Column(ARRAY(Integer, dimensions=1))
    total = Column(Integer)


    def __init__(self, stock=[]):
        self.stock = stock
        self.total = 0

if __name__ == '__main__':
    Base.metadata.create_all(db)

    session.add_all([P([1, 2]), P([0, 0]), P([0, 2])])
    session.commit()

    _q = select([F.sum(column('foo'))]) \
        .select_from(F.unnest('stock').alias('foo')).as_scalar()

    q = select([_q]).select_from(P.__table__)

    print session.execute(q).fetchall()

Answer 1

stock needs to be a column:

F.unnest(P.stock)

You passed a string bind argument.