SQLAlchemy import tables with relationships
I have problem with separating tables with relationships in different files. I want the tables below to be in three separate files and to import TableA in third party page, but I can not manage the load order.
In most of the time I'm receiving the following error.
sqlalchemy.exc. InvalidRequestError: When initializing mapper Mapper|TableA|tablea, expression 'TableB' failed to locate a name ("name 'TableB' is not defined"). If this is a class name, consider adding this relationship() to the class after both dependent classes have been defined.
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)
This should work (note that the TableC. table is replaced with the name of the table to avoid circular module loading):
### 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)
Also I believe that the ForeignKey parameter is case sensitive, so you code might not work because "TableA.id" doe snot match "tablea" name when case-sensitive.
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