Use the SQLAlchemy session in custom Flask-SQLAlchemy query method

Question

I would like to create a custom method to tell me whether a row exists in my database. The SQLAlchemy exists method returns a subquery but doesn't execute anything, so I wanted to create the method does_exist, which will simply return True or False. Here is my code:

from flask_sqlalchemy import SQLAlchemy, BaseQuery, Model

class CustomBaseQuery(BaseQuery):
    def does_exist(self):
        return db.session.query(self.exists()).scalar()

db = SQLAlchemy(app, query_class=CustomBaseQuery)

This actually does work, but it seems wrong to refer to db.session within the body of the method, which thus depends on later naming the SQLAlchemy instance db. I would like to find a way to reference the eventual db.session object in a more general way.

Full working example here: https://gist.github.com/wbruntra/3db7b630e6ffb86fe792e4ed5a7a9578

Ilja Everilä · Accepted Answer · 2018-05-31 09:04:25Z

2

Though undocumented, the session used by the Query object is accessible as

self.session

so your more generic CustomBaseQuery could look like

class CustomBaseQuery(BaseQuery):
    def does_exist(self):
        return self.session.query(self.exists()).scalar()

answered May 31, 2018 at 9:04

Ilja Everilä

53.4k9 gold badges138 silver badges142 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Use the SQLAlchemy session in custom Flask-SQLAlchemy query method

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related