Question

我一直在观看一些视频和阅读各种帖子，试图在python脚本中理解SQLAlchemy的基本结构。

任何人都可以告诉我：

以下脚本失败的原因

脚本：

from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Records(Base):
    __tablename__ = 'records'

    data1 = Column(Text())
    data2 = Column(Text())
    data3 = Column(Text())
    data4 = Column(Text())



if __name__ == "__main__":
    engine = create_engine('mysql://user:password@localhost/database')
    Base.metadata.create_all(bind=engine, checkfirst=True)

失败

Traceback (most recent call last):
  File "sqltest.py", line 6, in <module>
    class Records(Base):
  File "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/api.py", line 55, in __init__
  File "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 88, in _as_declarative
  File "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 103, in setup_mapping
  File "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 135, in __init__
  File "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 138, in _early_mapping
  File "build/bdist.linux-x86_64/egg/sqlalchemy/ext/declarative/base.py", line 530, in map
  File "<string>", line 2, in mapper
  File "build/bdist.linux-x86_64/egg/sqlalchemy/orm/mapper.py", line 629, in __init__
  File "build/bdist.linux-x86_64/egg/sqlalchemy/orm/mapper.py", line 1223, in _configure_pks
sqlalchemy.exc.ArgumentError: Mapper Mapper|Records|records could not assemble any primary key columns for mapped table 'records'

我被迫使用主键吗？或者这与我调用记录类的方式有关吗？

Answer 1

由于错误消息表明主键是必需的。没有理由不提供任何一个，否则你将无法表达任何表关系。

回应你的评论：如果您依赖于使用缺少主键的现有数据库方案，您可以尝试zzzeek（SQLAlchemy的作者）在他对此问题的评论中提出的内容：SQLAlchemy declarative: table without any primary keys?，因此使用例如

__mapper_args__ = {"primary_key":(data1, data2)}}

if（data1，data2）标识表行。并且应该有一种方法来识别表格行，否则你会遇到严重的设计问题。

Answer 2

感谢核子，我将Class移动到这个primary_key类，并指定data1列是一个长度为17的String，以便它成为主键。

from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Records(Base):
    __tablename__ = 'records'

    data1 = Column(String(17), primary_key=True)
    data2 = Column(Text())
    data3 = Column(Text())
    data4 = Column(Text())

if __name__ == "__main__":
    engine = create_engine('mysql://user:passwd@localhost/database')
    Base.metadata.create_all(bind=engine, checkfirst=True)

Python SQLAlchemy基本结构

2 个答案: