[英]SQLAlchemy - relationship limited on more than just the foreign key
I have a wiki db layout with Page
and Revisions
. 我有一个带有
Page
和Revisions
的wiki db布局。 Each Revision has a page_id
referencing the Page, a page
relationship to the referenced page; 每个版本都有一个引用页面的
page_id
,一个与引用页面的page
关系; each Page has a all_revisions
relationship to all its revisions. 每个页面都与其所有修订版具有
all_revisions
关系。 So far so common. 到目前为止很常见。
But I want to implement different epochs for the pages: If a page was deleted and is recreated, the new revisions have a new epoch
. 但是我想为页面实现不同的时期:如果页面被删除并重新创建,则新的修订版本将有一个
epoch
。 To help find the correct revisions, each page has a current_epoch
field. 为帮助找到正确的修订版,每个页面都有一个
current_epoch
字段。 Now I want to provide a revisions
relation on the page that only contains its revisions, but only those where the epochs match. 现在,我想在页面上提供仅包含其修订版本的
revisions
关系,但仅包含与历元记录匹配的revisions
关系。
This is what I've tried: 这就是我尝试过的:
revisions = relationship('Revision',
primaryjoin = and_(
'Page.id == Revision.page_id',
'Page.current_epoch == Revision.epoch',
),
foreign_keys=['Page.id', 'Page.current_epoch']
)
Full code (you may run that as it is) 完整代码 (您可以按原样运行)
However this always raises ArgumentError: Could not determine relationship direction for primaryjoin condition ...` , I've tried all I had come to mind, it didn't work. 然而,这总是引发ArgumentError:无法确定主连接条件的关系方向......` ,我已经尝试了所有我想到的,它没有用。
What am I doing wrong? 我究竟做错了什么? Is this a bad approach for doing this, how could it be done other than with a relationship?
这样做是不是一个糟糕的方法,除了关系之外怎么办呢?
Try installing relationship after both classes are created: 创建两个类后尝试安装关系:
Page.revisions = relationship(
'Revision',
primaryjoin = (Page.id==Revision.page_id) & \
(Page.current_epoch==Revision.epoch),
foreign_keys=[Page.id, Page.current_epoch],
uselist=True,
)
BTW, your test is not correct: revisions
property loads data from database while you haven't added them to session. 顺便说一句,您的测试不正确:
revisions
属性在您尚未将数据添加到会话时从数据库加载数据。
Update : The problem in your code is that primaryjoin
parameter is not string, so it's not evaluated . 更新 :代码中的问题是
primaryjoin
参数不是字符串,因此不进行评估 。 Using string in primaryjoin
works fine: 在
primaryjoin
使用string工作正常:
class Page(Base):
# [skipped]
revisions = relationship(
'Revision',
primaryjoin = '(Page.id==Revision.page_id) & '\
'(Page.current_epoch==Revision.epoch)',
foreign_keys=[id, current_epoch],
uselist=True,
)
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