python - 列 "Column"必须出现在 GROUP BY 子句中 -- SQLAlchemy

Question

尽管我在 group_by 中提到了上述列，但为什么我会收到标题错误。以下是我的查询

products = session
               .query(User) \
               .join(User.products) \
               .join(Product.productitems) \
               .values( Product.title.label('title'),(func.count(ProductItem.id)).label('total')) \
               .group_by(Product.id,Product.title) \
               .order_by(Product.created_date)

模型类

class User(UserMixin , Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    title = Column(CHAR(3), nullable = True)

class Product(Base):
    __tablename__ = 'products'
    id = Column(Integer, primary_key =True)
    title = Column(String(250), nullable = False)
    ..
    user_id = Column(Integer, ForeignKey('users.id'))
    user = relationship('User',backref=backref("products", cascade="all, delete-orphan"),lazy='joined')

class ProductItem(Base):
    __tablename__ ='product_items'
    id = Column(Integer , primary_key = True)
    ...
    product_id = Column(Integer, ForeignKey('products.id'))
    product = relationship('Product',backref=backref("productitems", cascade="all, delete-orphan"),lazy='joined' )

从控制台，我可以看到查询返回

SELECT 
    products.title AS title
   ,COUNT(product_items.id) AS total 
FROM 
    users 
        JOIN products ON users.id = products.user_id 
        JOIN product_items ON products.id = product_items.product_id

然后在 group_by 上出现错误而中断。请问这是什么要求？任何帮助将不胜感激。

Answer 1

SQLalchemy 要求 values 是链中的最后一件事，因为它不返回查询以继续。您需要做的可能是(未经测试的)；

products = session.query(User)                                               \
                  .join(User.products)                                       \
                  .join(Product.productitems)                                \
                  .group_by(Product.id, Product.title, Product.created_date) \
                  .order_by(Product.created_date)                            \
                  .values( Product.id.label('id'),                           \
                           Product.title.label('title'),                     \      
                           (func.count(ProductItem.id)).label('total'))