Python SQLAlchemy: AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'

Question

我尝试在我的项目中创建一个新数据库，但是当我运行脚本时出现这个错误，我有另一个项目使用类似的定义，它以前工作过，但现在出现同样的错误. 我使用的是 Python 2.7.8，SQLAlchemy 模块的版本是 0.9.8。顺便说一句，一个项目使用了Flask-SQLAlchemy，效果很好。我很困惑。追溯信息如下：

Traceback (most recent call last):
  File "D:/Projects/OO-IM/db_create.py", line 4, in <module>
    from models import Base
  File "D:\Projects\OO-IM\models.py", line 15, in <module>
    Column('followed_id', Integer(), ForeignKey('user.id'))
  File "C:\Python27\lib\site-packages\sqlalchemy\sql\schema.py", line 369, in __new__
    schema = metadata.schema
  File "C:\Python27\lib\site-packages\sqlalchemy\sql\elements.py", line 662, in __getattr__
    key)
AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'


from sqlalchemy import create_engine, Column, String, Integer, Text, DateTime, Boolean, ForeignKey, Table
from sqlalchemy.orm import sessionmaker, relationship, backref
from sqlalchemy.ext.declarative import declarative_base

SQLALCHEMY_DATABASE_URI = "mysql://root:mysqladmin@localhost:3306/oo_im?charset=utf8"

Base = declarative_base()

# TODO:AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'
friendships = Table('friendships',
                    Column('follower_id', Integer(), ForeignKey('user.id')),
                    Column('followed_id', Integer(), ForeignKey('user.id'))
)


class User(Base):
    __tablename__ = 'user'
    id = Column(Integer(), primary_key=True)
    account = Column(String(32), unique=True, nullable=False)
    password = Column(String(32), nullable=False)
    followed = relationship("User",
                            secondary=friendships,
                            primaryjoin=(friendships.c.follower_id == id),
                            secondaryjoin=(friendships.c.followed_id == id),
                            backref=backref("followers", lazy="dynamic"),
                            lazy="dynamic")

    def __init__(self, account, password, followed=None):
        self.account = account
        self.password = password

        if followed:
            for user in followed:
                self.follow(user)

    def follow(self, user):
        if not self.is_following(user):
            self.followed.append(user)
            return self

    def unfollow(self, user):
        if self.is_following(user):
            self.followed.remove(user)
            return self

    def is_following(self, user):
        return self.followed.filter(friendships.c.followed_id == user.id).count() > 0


class ChatLog(Base):
    __tablename__ = 'chatlog'
    id = Column(Integer(), primary_key=True)
    sender_id = Column(Integer(), ForeignKey('user.id'), nullable=False)
    receiver_id = Column(Integer(), ForeignKey('user.id'), nullable=False)
    send_time = Column(DateTime(), nullable=False)
    received = Column(Boolean(), default=False)
    content = Column(Text(), nullable=False)


engine = create_engine(SQLALCHEMY_DATABASE_URI, convert_unicode=True)
DBSession = sessionmaker(bind=engine)

Answer 1

table 定义应该是：

friendships = Table('friendships',
                    Base.metadata,
                    Column('follower_id', Integer(), ForeignKey('user.id')),
                    Column('followed_id', Integer(), ForeignKey('user.id'))
)

使用声明式语法定义table时，元数据通过class声明继承自Base，即

Base = declarative_base()

class ChatLog(Base)

但是，当使用旧的 Table 语法定义 table 时，必须明确指定元数据。

Answer 2

我有同样的错误，因为我用小写 c 拼写了 Column。应该是 Column.

Answer 3

我遇到了类似的问题。准确地说，我遇到的错误是： AttributeError: Neither 'ColumnClause' object nor 'Comparator' object has an attribute '_set_parent_with_dispatch'

经过一番努力，我发现这是一个拼写错误。我拼写 sa.Column 为 sa.column 在下面的代码片段行 #6.

from alembic import op
import sqlalchemy as sa

def something():
    op.add_column('table_name',
        sa.Column('column_name', sa.Text(), nullable=True) # Correct usage
    )

Python SQLAlchemy: AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'

Python SQLAlchemy: AttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'schema'

python

sqlalchemy

attributeerror