Question

我正在尝试创建一个查询来根据体重排序小狗列表，但是它不起作用，我收到以下错误

sqlalchemy.exc.InvalidRequestError: SQL expression, column, or mapped entity exp
ected - got '<database_setup.Puppy object at 0x02B7E590>'

来自同一个类的其他变量被正确排序而没有错误，我的代码如下所示

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

from database_setup import *
#from flask.ext.sqlalchemy import SQLAlchemy
from random import randint
import datetime
import random


engine = create_engine('sqlite:///puppies.db')

Base.metadata.bind = engine

DBSession = sessionmaker(bind=engine)

session = DBSession()


#Format for query 
#session.query(*table*)self.filter_by(*criteria*)

# 1. Query all of the puppies and return the results in ascending alphabetical order

#so we call a query on the Shelter table where we order by name
SheltersAlphabetically = session.query(Shelter).order_by(Shelter.name.desc())

for Shelter in SheltersAlphabetically:
    print Shelter.name

print '\n'
# 2. Query all of the puppies that are less than 6 months old organized by the youngest first
today = datetime.date.today()


PuppiesByAge = session.query(Puppy).filter(Puppy.dateOfBirth > '2014-12-03').order_by(Puppy.dateOfBirth)

for Puppy in PuppiesByAge:
    print Puppy.dateOfBirth

print '\n'

# 3. Query all puppies by ascending weight

PuppiesByWeight = session.query(Puppy).order_by(Puppy.weight)

for Puppy in PuppiesByWeight:
    print Puppy.weight

我的原始设置文件如下所示

import os 
import sys #provides key functions and variables

from sqlalchemy import Column, ForeignKey, Integer, String #good for mapper ode

from sqlalchemy.ext.declarative import declarative_base #used for config and class code

from sqlalchemy.orm import relationship #for foreign key relationships n mampper

from sqlalchemy import create_engine  # for config code

Base = declarative_base() # an instance of class we jsut improted,
                          #lets sql alchemy know our classes are special 
                          #sql alchemy classes, correspond to tables in databae

class Shelter (Base):
    __tablename__ =  'shelter'
    name = Column ( String(200), nullable = False)
    id = Column (Integer, primary_key = True)
    address = Column ( String(200), nullable = True)
    city = Column ( String(100), nullable = True)
    state = Column ( String(100), nullable = True)
    zipCode = Column ( String(100), nullable = True)
    website = Column ( String(200), nullable = True)

class Puppy (Base):
    __tablename__ = 'puppy'
    name = Column ( String(80), nullable = False)
    id = Column (Integer, primary_key = True)
    dateOfBirth = Column ( Integer, nullable = True)
    breed = Column ( String(100), nullable = True)
    gender = Column ( String(100), nullable = True)
    picture = Column ( String(300), nullable = True)
    weight = Column ( Integer, nullable = True)
    shelter_id = Column ( Integer, ForeignKey('shelter.id'))
    shelter = relationship(Shelter)

#database creation and class integration
engine = create_engine('sqlite:///puppies.db')

Base.metadata.create_all(engine)

如何避免此错误并执行查询以订购权重？

Answer 1

不要使用本地变量名Puppy - 已为您导入的Puppy类使用该名称。

我建议您在代码中代表小狗的变量使用puppy（全部小写）。

Python中的局部变量应按惯例使用小写：https://www.python.org/dev/peps/pep-0008/#method-names-and-instance-variables

SQLAlchemy查询中出现意外错误

1 个答案: