Question

我试图通过pyodbc和SQL Server与sqlalchemy建立多对多的关系，这是我的代码：

from sqlalchemy import Table, Text
from sqlalchemy import ForeignKey
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()
courses_students = Table('courses_students',Base.metadata,
                        Column('stu_id',ForeignKey('student.id'),primary_key=True),
                        Column('cour_id',ForeignKey('course.id'),primary_key=True),
                        Column('grade',Integer())
    )

# from sqlalchemy.ext.declarative import declarative_base
# Base = declarative_base()

class Student(Base):
    __tablename__ = 'student'

    stu_id = Column('id',Integer,primary_key=True)
    name = Column('name',String(10))
    stu_class = Column('class',String(10))
    #courses = relationship('Course',secondary=courses_students,back_populates='students')

    def __init__(self,stu_id,name,stu_class):
        self.stu_id = stu_id
        self.name = name
        self.stu_class = stu_class

    def __repr__(self):
        _str = "Student({_id},{_name},{_class})".format(_id=self.stu_id,_name=self.name,
                                                        _class=self.stu_class)
        return _str

# from sqlalchemy.ext.declarative import declarative_base
# Base = declarative_base()

class Course(Base):
    __tablename__ = 'course'

    cour_id = Column('id',Integer,primary_key=True)
    name = Column('name',String(20))
    teacher_name = Column('teacher_name',String(10))
    credit = Column('credit',Integer())

    students = relationship('Student',secondary=courses_students,backref='courses')

    def __init__(self,c_id,name,t_name,credit):
        self.cour_id = c_id
        self.name = name
        self.teacher_name = t_name
        self.credit = credit

    def __repr__(self):
        _str = "Course({_id},{_na},{_t_na},{_cre})".format(_id=self.cour_id,_na=self.name,
                                                          _t_na=self.teacher_name,
                                                          _cre=self.credit)
        return _str

但是，当我尝试使用session.add()添加数据时，我遇到了以下错误：

InvalidRequestError：一个或多个映射器无法初始化 - 无法继续初始化其他映射器。触发映射器：＆＃39;映射器|学生|学生＆＃39;。最初的例外是：初始化mapper Mapper | Student | student，expression＆＃39; course＆＃39;找不到姓名（＆＃34;名称＆＃39;当然＆＃39;未定义＆＃34;）。如果这是一个类名，请考虑在定义了两个依赖类之后将此关系（）添加到类中。

Answer 1

该特定错误是由输入错误和您在评论之前创建的单独Base类引起的。我假设模型定义最初是在单独的文件中。

relationship()需要映射的类或解析为第一个参数的字符串，但是您传递了它'course'，它解析为该类映射到的Table。在您的示例中，您似乎已更正了对'Course'的引用。

命名传递给relationship()的类的字符串参数在mapper compilation time期间通过从与Base关联的类注册表中查找来解析。但是在您的示例中，您为每个模型和关联Base创建了单独的Table类，因此查找失败，因为这些类都位于不同的注册表中。

第一次使用Session时会引发错误，因为mappers是懒惰配置的。另外，configure_mappers()可用于显式配置任何挂起的更改。

您的Course定义中存在另一个错误：而不是back_populates='courses'您已使用backref='courses'，因此在配置过程中会出现以下错误：< / p>

Traceback (most recent call last):
  File "wtf.py", line 60, in <module>
    configure_mappers()
  File "~/Work/sqlalchemy/lib/sqlalchemy/orm/mapper.py", line 3029, in configure_mappers
    mapper._post_configure_properties()
  File "~/Work/sqlalchemy/lib/sqlalchemy/orm/mapper.py", line 1828, in _post_configure_properties
    prop.init()
  File "~/Work/sqlalchemy/lib/sqlalchemy/orm/interfaces.py", line 184, in init
    self.do_init()
  File "~/Work/sqlalchemy/lib/sqlalchemy/orm/relationships.py", line 1659, in do_init
    self._generate_backref()
  File "~/Work/sqlalchemy/lib/sqlalchemy/orm/relationships.py", line 1849, in _generate_backref
    (backref_key, self, m))
sqlalchemy.exc.ArgumentError: Error creating backref 'courses' on relationship 'Course.students': property of that name exists on mapper 'Mapper|Student|student'

使用SQLAlchemy和SQL Server向数据库添加数据时出现InvalidRequestError

1 个答案: