我的SQLAlchemy结构如下所示

papers2authors_table = Table('papers2authors', Base.metadata,
    Column('paper_id', Integer, ForeignKey('papers.id')),
    Column('author_id', Integer, ForeignKey('authors.id'))
)

class Paper(Base):
    __tablename__ = "papers"

    id = Column(Integer, primary_key=True)
    title = Column(String)
    handle = Column(String)

    authors = relationship("Author",
                    secondary="papers2authors",
                    backref="papers")

class Author(Base):
    __tablename__ = "authors"

    id = Column(Integer, primary_key=True)
    name = Column(String, unique=True)
    code = Column(String, unique=True)

我想查询两件事：

1. 每篇论文的作者人数
2. 每位作者的论文数

我尝试了func.count()和的许多选择count()，但它们返回的结果毫无意义。如何以SQLAlchemy方式完成这两件事？

我尝试了什么

• db.s.query(func.count(core.Paper.id)).group_by(core.Author.id).first() = sqlalchemy.exc.OperationalError: (OperationalError) no such column: authors.id
• db.s.query(func.count(core.Author.papers)).group_by(core.Author.id).first()= (128100)，这不是我期望的
• db.s.query(core.Author.papers).group_by(core.Author.id).count().first() = AttributeError: 'int' object has no attribute 'first'
• …