SQLAlchemy等效于Django ORM的关系扩展过滤器 [英] SQLAlchemy equivalent of Django ORM's relationship-spanning filter
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问题描述
此示例来自 Django文档。
给出(Django)数据库模型:
Given the (Django) database model:
class Blog(models.Model):
name = models.CharField(max_length=100)
class Entry(models.Model):
blog = models.ForeignKey(Blog)
headline = models.CharField(max_length=255)
body_text = models.TextField()
在Django中我可以使用:
In Django I can use:
Entry.objects.filter(blog__name__exact='Beatles Blog')
获取具有指定名称的博客的所有 Entry
对象。
to get all Entry
objects for blogs with the specified name.
问题:给定以下模型定义,等效的SQLAlchemy语句是什么?
Question: What is the equivalent SQLAlchemy statement, given the model definition below?
class Blog(Base):
__tablename__ = "blog"
id = Column(Integer, primary_key=True)
name = Column(Unicode(100))
class Entry(Base):
__tablename__ = "entry"
id = Column(Integer, primary_key=True)
blogid = Column(Integer, ForeignKey(Blog.id))
headline = Column(Unicode(255))
body_text = Column(UnicodeText)
blog = relationship(Blog, backref="entries")
编辑
我相信有两种方法可以完成此操作:
I believe there are two ways to accomplish this:
>>> q = session.query
>>> print q(Entry).join(Blog).filter(Blog.name == u"One blog")
SELECT entry.id AS entry_id, entry.blogid AS entry_blogid, entry.headline AS entry_headline, entry.body_text AS entry_body_text
FROM entry JOIN blog ON blog.id = entry.blogid
WHERE blog.name = ?
>>> print q(Entry).filter(Entry.blog.has(Blog.name == u"One blog"))
SELECT entry.id AS entry_id, entry.blogid AS entry_blogid, entry.headline AS entry_headline, entry.body_text AS entry_body_text
FROM entry
WHERE EXISTS (SELECT 1
FROM blog
WHERE blog.id = entry.blogid AND blog.name = ?)
# ... and of course
>>> blog = q(Blog).filter(Blog.name == u"One blog")
>>> q(Entry).filter(Entry.blog == blog)
还有几个问题:
- 除了上述方法以外,还有其他方法可以使用SQLAlchemy完成此操作吗?
- 是否没有道理是否可以在多对一关系中执行
session.query(Entry).filter(Entry.blog.name == u一个博客)
? - 在这种情况下Django的ORM生成什么SQL?
推荐答案
怎么样:
session.query(model.Entry).join((model.Blog, model.Entry.blogid==model.Blog.id)).filter(model.Blog.name=='Beatles Blog').all()
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