计算SQLAlchemy中的关系

Question

我的SQLAlchemy结构看起来像这样

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. 每篇论文中的作者数量
2. 论文中的数字每笔者(部分回答了在这里)

我试着用很多选项func.count()和count(),但他们返回无意义的结果.如何以SQLAlchemy的方式做这两件事？

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),这不是我的预期
• db.s.query(core.Author.papers).group_by(core.Author.id).count().first() = AttributeError: 'int' object has no attribute 'first'
• ...

Answer 1

找到解决方案:

1. 每篇论文的作者数量: db.s.query(core.Paper.title, func.count(core.Author.id)).join(core.Paper.authors).group_by(core.Paper.id).all()
2. 每位作者的论文数量: db.s.query(core.Author.name, func.count(core.Author.id)).join(core.Author.papers).group_by(core.Author.id).all()

相关:http://docs.sqlalchemy.org/en/rel_0_9/orm/query.html#sqlalchemy.orm.query.Query.having