Flask SQL Alchemy with declarative ORM extension

Question

I am using sqlalchemy ORM with declarative extensions in a Flask project for a web API. The Flask documentation shows how to execute query properly inside an endpoint here

Now this is all good, but what if i want to execute a group by query. For example given the user domain object in the flask documentation:

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String(50), unique=True)
    email = Column(String(120), unique=True)

I want to retrieve the sum of ids for all the users with the same name (doesn't make sense, take it as toy example for sake of simplicity!). In pure SQL i could do it easily with:

select name, sum(id) from user group by name

However inside an endpoint the reccomanded way to execute a query (again see here ) is to start from a ref to the domain object User, for instance:

User.query.filter(User.name == 'admin').first()

To execute a group-by query I would rather use something like this (which indeed works!):

#see database module http://flask.pocoo.org/docs/0.12/patterns/sqlalchemy/#declarative)
from database import db_session 

 @app.route('/')
 def index():
     db_session.query(func.sum(User.id).label('num_id'), User.name).group_by(User.name).all()

In this case the query starts from db_session. Is this correct and safe? Remeamber we are in a concurrent application inside Flask.

Any help?

Answer 1

It's fine. But I usually use . with_entities(*entities) for such cases:

User.query.filter(filters).with_entities(User.name.label('name'), func.count(User.id).label('count')).group_by(User.name)