Python Sqlalchemy一对多关系加入?
我正在尝试这样做一个简单的连接查询Python Sqlalchemy一对多关系加入?,python,sqlalchemy,flask,flask-sqlalchemy,Python,Sqlalchemy,Flask,Flask Sqlalchemy,我正在尝试这样做一个简单的连接查询 SELECT food._id, food.food_name, food_categories.food_categories FROM food JOIN food_categories ON food.food_category_id = food_categories._id 但是不断地收到一个错误。下面是如何设置我的类 class Food_Categories(db.Model): __tablename__ = 'food_catego
SELECT food._id, food.food_name, food_categories.food_categories FROM food JOIN food_categories ON food.food_category_id = food_categories._id
但是不断地收到一个错误。下面是如何设置我的类
class Food_Categories(db.Model):
__tablename__ = 'food_categories'
_id = db.Column(db.Integer, primary_key=True)
food_categories = db.Column(db.String(30))
class Food(db.Model):
__tablename__ = 'food'
_id = db.Column(db.Integer, primary_key=True)
food_name = db.Column(db.String(40))
food_category_id = db.Column(db.Integer, ForeignKey(Food_Categories._id))
food_category = relationship("Food_Categories")
我的查询函数如下所示
@app.route('/foodlist')
def foodlist():
if request.method == 'GET':
results = Food.query.join(Food_Categories.food_categories).all()
json_results = []
for result in results:
d = {'_id': result._id,
'food': result.food_name,
'food_category': result.food_categories}
json_results.append(d)
return jsonify(user=json_results)
我用的是烧瓶。当我调用路由时,我得到了这个错误
AttributeError: 'ColumnProperty' object has no attribute 'mapper'
我基本上想要这个:
| id | food_name | food_category |
并将食品类别id列替换为其他表中食品类别的实际名称
我的表/关系设置是否正确?我的查询设置正确吗 您的表和关系设置正确。您的查询需要更改 出现错误的原因是您试图对列(
Food\u Categories.Food\u Categories
)而不是表(或映射的模型对象)执行联接。从技术上讲,您应该将查询替换为以下查询以修复错误:
results = Food.query.join(Food_Categories).all()
这将修复错误,但不会生成所需的SQL
语句,因为即使存在联接,它也只会作为结果返回Food
的实例
为了构建一个能够准确生成您心目中的SQL
语句的查询:
results = (db.session.query(Food._id, Food.food_name,
Food_Categories.food_categories,)
.join(Food_Categories)).all()
for x in results:
# print(x)
print(x._id, x.food_name, x.food_categories)
请注意,在这种情况下,结果不是食品
的实例,而是具有3列值的元组