我是SQLAlchemy的新手。我在应用程序中建立两个模型之间的一对多关系时遇到了一些困难。我有两个模型User`Photo'。用户只有一个与之关联的角色，而角色有许多与之关联的用户。
这是我在data_generator.py文件中的代码：
# coding=utf-8
from sqlalchemy import Column, Integer, String, BigInteger,Date, Enum, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
import time
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, relationship
import datetime
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
id = Column(Integer(), primary_key=True)
username = Column(String(30), unique=True, nullable=False)
password = Column(String, default='123456', nullable=False)
name = Column(String(30), nullable=False)
grade = Column(String(30))
emp_no = Column(BigInteger, unique=True, nullable=False)
roles = relationship('Role', back_populates='users')
class Scene(Base):
__tablename__ = 'scenes'
id = Column(Integer, primary_key=True)
scene_name = Column(String(30), nullable=False)
life_time = Column(Date, nullable=False,
default=datetime.datetime.strptime(
time.strftime("%Y-%m-%d", time.localtime(time.time() + (12 * 30 * 24 * 3600))),'%Y-%m-%d').date())
scene_description = Column(String(150), default="")
class Gateway(Base):
__tablename__ = 'gateways'
id = Column(Integer, primary_key=True)
gateway_name = Column(String(30), nullable=False)
gateway_api_key = Column(String(100), nullable=False, unique=True)
gateway_type = Column(Enum('up', 'down', 'soft', name="gateway_type"), nullable=False)
class Role(Base):
__tablename__ = 'roles'
id = Column(Integer, primary_key=True)
role_name = Column(String(30), unique=True, nullable=False)
users = relationship('User', back_populates='roles')
def __repr__(self):
return self.role_name
engine = create_engine('sqlite:///memory:')
Session = sessionmaker()
Session.configure(bind=engine)
session = Session()
Base.metadata.create_all(engine)
ed_user = User(name='ed', username='jack', password='123', emp_no=1, grade='1', roles=1)
example_scene = Scene(scene_name='example_1', scene_description='example_description')
example_gateway = Gateway(gateway_name='example_1',gateway_api_key='11111',gateway_type='up')
# session.add(example_gateway)
# session.commit()
def init_user(flag, number):
while number >= 1:
if flag == 1:
ed_user = User(name='ed', username='jack', password='123', emp_no=1, grade='1')
pass
if flag == 2:
# TODO admin
pass
if flag == 3:
# TODO teacher
pass
number -= 1
def init_scene(number):
while number >= 1:
number -= 1
# TODO scene
def init_gateway(api_key, number):
# TODO gateway
pass
if __name__ == '__main__':
with session.no_autoflush:
c = session.query(Gateway).all()
print c[0].id
我遇到的错误如下所示：
/usr/bin/python2.7 /home/pajamas/PycharmProjects/untitled5/data_generator.py
Traceback (most recent call last):
File "/home/pajamas/PycharmProjects/untitled5/data_generator.py", line 73, in <module>
ed_user = User(name='ed', username='jack', password='123', emp_no=1, grade='1', roles=1)
File "<string>", line 2, in __init__
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", line 347, in _new_state_if_none
state = self._state_constructor(instance, self)
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 764, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", line 177, in _state_constructor
self.dispatch.first_init(self, self.class_)
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/event/attr.py", line 256, in __call__
fn(*args, **kw)
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 3088, in _event_on_first_init
configure_mappers()
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 2984, in configure_mappers
mapper._post_configure_properties()
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 1810, in _post_configure_properties
prop.init()
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/interfaces.py", line 184, in init
self.do_init()
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1658, in do_init
self._setup_join_conditions()
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1733, in _setup_join_conditions
can_be_synced_fn=self._columns_are_mapped
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1991, in __init__
self._determine_joins()
File "/home/pajamas/.local/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 2096, in _determine_joins
"specify a 'primaryjoin' expression." % self.prop)
sqlalchemy.exc.NoForeignKeysError: Could not determine join condition between parent/child tables on relationship User.roles - there are no foreign keys linking these tables. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.
Process finished with exit code 1
有人可以帮助我吗？非常感谢帮助。
答案 0 :(得分：4)
用户和角色之间可能存在三种关系：
一对一：
class Role(Base):
id = Column(Integer, primary_key=True)
# ...
user_id = Column(Integer, ForeignKey("user.id"))
class User(Base):
id = Column(Integer, primary_key=True)
# ...
role = relationship("Role", back_populates="user", uselist=False)
对于多对一：
class Role(Base):
id = Column(Integer, primary_key=True)
# ...
user_id = Column(Integer, ForeignKey("user.id"))
class User(Base):
id = Column(Integer, primary_key=True)
# ...
roles = relationship("Role", back_populates="user")
对于多对多:(在这种关系中，我们需要一个关联表）
roles_users = Table("roles_users",
Column("role_id", Integer, ForeignKey("role.id")),
Column("user_id", Integer, ForeignKey("user.id")))
class Role(Base):
id = Column(Integer, primary_key=True)
# ...
class User(Base):
id = Column(Integer, primary_key=True)
# ...
roles = relationship("Role", back_populates="users", secondary=roles_users)
答案 1 :(得分：0)
由于缺乏数据库和SQL炼金术，我犯了一个低级别的错误。 首先，这是典型的“一对多”问题。关系通过用户的外键连接两个表中的两行。 role_id被定义为构建连接的外键。 “ForeignKey（）”中的参数“roles.id”阐明了此列是Role的行的id relationship（）的backref专门用于角色模型。