How to query for empty records in many to many relation

问题

class BlogPost(SchemaBase):
  id = Column(Integer, primary_key=True)
  name    = Column(String,  unique=True)
  authors = relationship('Authors', secondary='authors_to_blog_post')
  __tablename__ = 'blogpost'

class Authors(SchemaBase):
  id = Column(Integer, primary_key=True)
  name    = Column(String,  unique=True)
  __tablename__ = 'author'

authors_to_blog_post = Table('authors_to_blog_post', Base.metadata,
    Column('author_id', Integer, ForeignKey('author.id')),
    Column('blogpost_id', Integer, ForeignKey('blogpost.id'))
    )

Now how to query for all blogposts without any author? session.query(BlogPost).filter(BlogPost.authors == []) doesnt work

回答1:

Found answer from here: https://groups.google.com/d/msg/sqlalchemy/Ow0bb6HvczU/VVQbtd7MnZkJ

So the solution is

session.query(BlogPost).filter(BlogPost.authors.any())

来源：https://stackoverflow.com/questions/23814431/how-to-query-for-empty-records-in-many-to-many-relation