sqlalchemy exists for query

Question

How do I check whether data in a query exists?

For example:

users_query = User.query.filter_by(email='x@x.com')

How I can check whether users with that email exist?

I can check this with

users_query.count()

but how to check it with exists?

Answer 1

The following solution is a bit simpler:

from sqlalchemy.sql import exists

print session.query(exists().where(User.email == '...')).scalar()

Answer 2

The most acceptable and readable option for me is

session.query(<Exists instance>).scalar()

like

session.query(User.query.filter(User.id == 1).exists()).scalar()

which returns True or False.

Answer 3

There is no way that I know of to do this using the orm query api. But you can drop to a level lower and use exists from sqlalchemy.sql.expression:

from sqlalchemy.sql.expression import select, exists

users_exists_select = select((exists(users_query.statement),)) 
print engine.execute(users_exists_select).scalar()