我正在开发一个广泛使用 sqlalchemy 的代码库，而且我是新手。我在为要编写的查询编写 sqlalchemy 表达式时遇到问题。
我们有以下 3 个表：
- 产品 -（product_id、product_description、status、available）
- 类别 - (category_id, category_description)
- ProductCategoryLink - (product_id, category_id) [对于多对多关系]
我正在运行一个查询，该查询为我提供了每个类别的产品数量。有些产品没有分配到任何类别，我也想要这些产品（在这种情况下，类别将为空）。我想出了以下查询
select c.category_name, count(p.product_id)
from Product as p
left join ProductCategoryLink as pc
on p.product_id = pc.product_id
left join Category as c
on c.category_id = pc.category_id
where p.store_id = 1111
and p.status = 'ACTIVE'
and p.available = 1
group by c.category_name;
我的 orm 文件中有以下映射
class Product(Base):
__tablename__ = 'Product'
product_id = Column(Integer, primary_key=True, name='product_id')
product_description = Column(UnicodeText, name='description')
available = Column(Boolean, name='available')
status = Column(Unicode(length=255), name='status')
metadata = Base.metadata
# association table between product and category
product_category_link = Table('ProductCategoryLink', metadata,
Column('product_id', Integer, ForeignKey('Product.product_id')),
Column('category_id', Integer, ForeignKey('Category.category_id'))
)
class Category(Base):
__tablename__ = 'Category'
category_id = Column(Integer, primary_key=True, name='category_id')
category_name = Column(Unicode(length=255), name='category_name')
products = relation('Product', secondary=product_category_link, backref='categories')
我想出了以下ORM表达式
query = session.query(Category.category_name, func.count(Product.product_id)).join(product_category_link).\
join(Category).filter(
and_(Product.store_id == self._store_id,
and_(Product.status == 'ACTIVE', Product.available == 1))).\
group_by(Category.category_name).all()
上面的表达式创建的 sql 查询不是我想要的。
sqlalchemy.exc.OperationalError: (OperationalError) (1066, "Not unique table/alias: 'Category'") 'SELECT `Category`.category_name AS `Category_category_name`, count(`Product`.product_id) AS count_1 \nFROM `Product`, `Category` INNER JOIN `ProductCategoryLink` ON `Category`.category_id = `ProductCategoryLink`.category_id INNER JOIN `Category` ON `Category`.category_id = `ProductCategoryLink`.category_id \nWHERE `Product`.store_id = %s AND `Product`.status = %s AND `Product`.available = %s GROUP BY `Category`.category_name' (1, 'ACTIVE', 1)
我在这里做错了什么？