人际关系SQLAlchemy的导入表(SQLAlchemy import tables with r

我有问题，在不同的文件中关系分离表。 我想下面的表格是在三个单独的文件，并导入第三方页表A，但我不能管理的加载顺序。

在大多数的时间我收到以下错误。

sqlalchemy.exc。 InvalidRequestError：当初始化映射器映射|表A | TableA的，表达“表B”未能找到（“名‘表B’没有定义”）的名称。 如果这是一个类名，都依赖类已经被定义后考虑加入这种关系（）的类。

class TableA(Base):
    __tablename__ = "tablea"
   id = Column(Integer, primary_key=True)
   name = Column(String)

   tableB = relationship("TableB", secondary = TableC.__table__)

class TableB(Base):
   __tablename__ = "tableb"
   id = Column(Integer, primary_key=True)
  name = Column(String)

class TableC(Base):
   __tablename__ = "tableab"
   tableAId = Column("table_a_id", Integer, ForeignKey("TableA.id"), primary_key=True)
   tableBId = Column("table_b_id", Integer, ForeignKey("TableB.id"), primary_key=True)

Answer 1:

这应该工作（注意，表C 表被替换为表的名称，以避免循环加载模块。）：

### base.py
engine = create_engine('sqlite:///:memory:', echo=True)
Session = sessionmaker(bind=engine)
Base = declarative_base(bind=engine)

### classA.py
from base import Base
from classB import TableB

class TableA(Base):
    __tablename__ = 'tablea'
    id = Column(Integer, primary_key=True)
    name = Column(String(50))
    tableBs = relationship("TableB", secondary="tableab")
    #tableBs = relationship("TableB", secondary=TableC.__table__)

### classB.py
from base import Base

class TableB(Base):
    __tablename__ = 'tableb'
    id = Column(Integer, primary_key=True)
    name = Column(String(50))

### classC.py
from base import Base
from classA import TableA
from classB import TableB

class TableC(Base):
    __tablename__ = 'tableab'
    tableAId = Column(Integer, ForeignKey("tablea.id"), primary_key=True, )
    tableBId = Column(Integer, ForeignKey("tableb.id"), primary_key=True, )

### main.py
from base import Base, Session, engine
from classA import TableA
from classB import TableB
from classC import TableC
Base.metadata.create_all(engine)

此外，我认为，ForeignKey的参数是大小写敏感的，所以你的代码可能无法工作，因为“TableA.id”母鹿鼻涕匹配“表A”名称时区分大小写。

Answer 2:

from sqlalchemy import Column, String, Integer
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()


class Parent(Base):
    __tablename__ = 'Parent'
    ParentID = Column(Integer, primary_key=True)
    Description = Column(String)

    def __init__(self, ParentID, Description):
        self.ParentID = ParentID
        self.Description = Description
----------------------------------------------------------------------

from sqlalchemy import Column, String, Integer, ForeignKey
import Parent
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()


class Child(Base):
    __tablename__ = "Child"
    ChildID = Column(Integer, primary_key=True)
    Description = Column(String)
    ParentID = Column('CompanyID', Integer, ForeignKey(Parent.ParentID))

    def __init__(self, ChildID, Description,ParentID):
        self.ChildID = ChildID
        self.Description = Description
        self.ParentID=ParentID

文章来源: SQLAlchemy import tables with relationships