python - sqlalchemy:使用声明和反射多次连接到同一个表

Question

这是我的问题的精简版:

假设我有两个表:“过程”和“角色”。

角色有字段:(role_uid, role_name)

过程有字段:(procedure_uid, procedure_name, inform_role_uid, consult_role_uid)

所以 'role' 与 'procedure' 有两个一对多的关系。

部分代码:

class Role(Base):
    __tablename__ = "role"
    __table_args__ = ({'autoload':True, 'useexisting': True})

class Procedure(Base):
    __tablename__ = "procedure"
    __table_args__ = (sqlalchemy.ForeignKeyConstraint(['consult_role_uid','inform_role_uid'],['role.role_uid', 'role.role_uid']),
        {'autoload':True, 'useexisting': True})

Procedure.consult_role = sqlalchemy.orm.relationship(Role,
 primaryjoin="Procedure.consult_role_uid==Role.role_uid", foreign_keys=Role.role_uid)
Procedure.inform_role = sqlalchemy.orm.relationship(Role,
 primaryjoin="Procedure.inform_role_uid==Role.role_uid", foreign_keys=Role.role_uid)

consult_role = sqlalchemy.orm.aliased(Role, name="consult_role")
inform_role = sqlalchemy.orm.aliased(Role, name="inform_role")

query = session.query(
    Procedure.procedure_name, 
    consult_role.role_name.label("consult_role_name"),
    inform_role.role_name.label("inform_role_name")).join(consult_role, inform_role)

这会产生以下 SQL:

SELECT 
  `procedure`.procedure_name AS procedure_procedure_name, 
  consult_role.role_name AS consult_role_name, 
  inform_role.role_name AS inform_role_name 
FROM 
  `procedure` 
  INNER JOIN role AS consult_role 
    ON consult_role.role_uid = `procedure`.consult_role_uid
      AND consult_role.role_uid = `procedure`.inform_role_uid 
  INNER JOIN role AS inform_role 
    ON inform_role.role_uid = `procedure`.consult_role_uid 
      AND inform_role.role_uid = `procedure`.inform_role_uid

如您所见，我无意让每个内部联接都加入两个字段。 为什么它似乎忽略了我的“primaryjoin”参数？

Answer 1

因此，为了完整起见，这里是上述问题的固定代码。我添加了两个 ForeignKeyContstaints，我还必须指定要在连接中使用的关系。

class Role(Base):
    __tablename__ = "role"
    __table_args__ = ({'autoload':True, 'useexisting': True})


class Procedure(Base):
    __tablename__ = "procedure"
    __table_args__ = (
        sqlalchemy.ForeignKeyConstraint(['consult_role_uid'], ['role.role_uid']),
        sqlalchemy.ForeignKeyConstraint(['inform_role_uid'], ['role.role_uid']),
        {'autoload':True, 'useexisting': True})

Procedure.consult_role = sqlalchemy.orm.relationship(Role,
 primaryjoin="Procedure.consult_role_uid==Role.role_uid", foreign_keys=Role.role_uid)
Procedure.inform_role = sqlalchemy.orm.relationship(Role,
 primaryjoin="Procedure.inform_role_uid==Role.role_uid", foreign_keys=Role.role_uid)

consult_role = sqlalchemy.orm.aliased(Role, name="consult_role")
inform_role = sqlalchemy.orm.aliased(Role, name="inform_role")

query = session.query(
    Procedure.procedure_name, 
    consult_role.role_name.label("consult_role_name"),
    inform_role.role_name.label("inform_role_name")).join((consult_role, Procedure.consult_role), (inform_role, Procedure.inform_role))

这产生了以下正确的 SQL:

SELECT 
  `procedure`.procedure_name AS procedure_procedure_name, 
  consult_role.role_name AS consult_role_name, 
  inform_role.role_name AS inform_role_name 
FROM 
  `procedure` 
  INNER JOIN role AS consult_role ON `procedure`.consult_role_uid = consult_role.role_uid     
  INNER JOIN role AS inform_role ON `procedure`.inform_role_uid = inform_role.role_uid