Sqlalchemy 存在联合继承和 Firebird答案

【问题标题】：Sqlalchemy exists with joined inheritance and FirebirdSqlalchemy 存在联合继承和 Firebird
【发布时间】：2012-05-28 20:29:54
【问题描述】：

我尝试使用sqlaclhemy连接表继承，出现了奇怪的情况。

class CommonObject(Base):
    __tablename__ = "objects"
    id = Column("objid", Integer, primary_key=True)
    objname = Column(String(32))
    ...    

class GoodsPlacement(Container, Loadable, Dumpable):
    __tablename__ = "goods_placements"
    id = Column("objid", Integer, ForeignKey("containers.objid"), primary_key=True)
    ...

class Departure(CommonObject):
     __tablename__ = "departures"
    id = Column(Integer, ForeignKey("objects.objid"),  primary_key=True)
    content_id = Column(Integer, ForeignKey("goods_placements.objid"))
    content = relationship("GoodsPlacement",
        primaryjoin="Departure.content_id==GoodsPlacement.id",
        foreign_keys=[content_id],
        lazy='joined',
        backref="departures")
    ...

当我写查询时：

session.query(GoodsPlacement).filter(~GoodsPlacement.departures.any(Departure.status_id < 2))

它给我带来了这样的东西：

SELECT 
    objects.objid AS objects_objid,
    goods_placements.objid AS goods_placements_objid,
    objects.objname AS objects_objname 
FROM objects
JOIN goods_placements ON objects.objid = goods_placements.objid 
WHERE NOT (EXISTS (
    SELECT 1 
    FROM (
        SELECT
            objects.objid AS objects_objid,
            objects.objname AS objects_objname,
            departures.id AS departures_id,
            departures.content_id AS departures_content_id,
            departures.status_id AS departures_status_id 
        FROM objects
        JOIN departures ON objects.objid = departures.id)
    AS anon_1, objects 
    WHERE anon_1.departures_content_id = objects.objid
        AND anon_1.departures_status_id < :status_id_1)
)

这不起作用，因为存在子句中的对象覆盖了外部对象。由于我使用的解决方法直接来自 sqlexpression，

session.query(GoodsPlacement).filter(~exists([1],
    and_("departures.status_id<2",
         "departures.content_id=goods_placements.objid"),
    from_obj="departures"))

但它很大程度上取决于列名和表名。

如何在exists语句中为对象表指定别名？

Debian wheezy，python-2.7.3rc2，sqlaclhemy 0.7.7-1

【问题讨论】：

能否请您添加query 定义的其余部分，而不仅仅是filter 部分。
session.query(GoodsPlacement).filter(...).all()
这些映射不完整。 GoodsPlacement 是 CommonObject 的子类吗？您能否制定一个完整的复制示例（不包括与错误生成的查询无关的内容）并通过电子邮件发送 SQLAlchemy 列表。连接表继承映射器之间的通用关系非常复杂。
门票已添加sqlalchemy.org/trac/ticket/2491 和sqlalchemy.org/trac/ticket/2492。直到 0.8 版本改进了 any() 的机制后，该错误才可能得到修复。

标签： python sqlalchemy exists declarative class-table-inheritance

【解决方案1】：

声明性系统在如何设置列方面存在一个错误。您为列提供的“objid”名称与“id”属性名称不同，是此处问题的根源。下面的测试用例近似于您的上述系统，并显示了一个解决方法，直到错误被修复：

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

Base= declarative_base()

class CommonObject(Base):
    __tablename__ = "objects"
    id = Column("objid", Integer, primary_key=True)
    objname = Column(String(32))

class Container(CommonObject):
    __tablename__ = 'containers'
    id = Column("objid", Integer, ForeignKey("objects.objid"),  primary_key=True)

class GoodsPlacement(Container):
    __tablename__ = "goods_placements"
    id = Column("objid", Integer, ForeignKey("containers.objid"), primary_key=True)


class Departure(CommonObject):
    __tablename__ = "departures"
    id = Column(Integer, ForeignKey("objects.objid"),  primary_key=True)
    content_id = Column(Integer, ForeignKey("goods_placements.objid"))
    status_id = Column(Integer)
    content = relationship("GoodsPlacement",
        primaryjoin=lambda:Departure.__table__.c.content_id==GoodsPlacement.__table__.c.objid,
        backref="departures"
        )

session = Session()
print session.query(GoodsPlacement).filter(~GoodsPlacement.departures.any(Departure.status_id < 2))

输出：

SELECT objects.objid AS objects_objid, containers.objid AS containers_objid, goods_placements.objid AS goods_placements_objid, objects.objname AS objects_objname 
FROM objects JOIN containers ON objects.objid = containers.objid JOIN goods_placements ON containers.objid = goods_placements.objid 
WHERE NOT (EXISTS (SELECT 1 
FROM (SELECT objects.objid AS objects_objid, objects.objname AS objects_objname, departures.id AS departures_id, departures.content_id AS departures_content_id, departures.status_id AS departures_status_id 
FROM objects JOIN departures ON objects.objid = departures.id) AS anon_1 
WHERE anon_1.departures_content_id = goods_placements.objid AND anon_1.departures_status_id < :status_id_1))

【讨论】：