sqlalchemy exists for query
PythonSqlalchemyExistsPython Problem Overview
How do I check whether data in a query exists?
For example:
users_query = User.query.filter_by(email='[email protected]')
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?
Python Solutions
Solution 1 - Python
The following solution is a bit simpler:
from sqlalchemy.sql import exists
print session.query(exists().where(User.email == '...')).scalar()
Solution 2 - Python
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.
Solution 3 - Python
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()
Solution 4 - Python
2021 Answer for SqlAlchemy 1.4
Refrain from calling .query method and use the select statement directly chained with the .exists method as follows:
from sqlalchemy import select
stmt = select(User).where(User.email=="[email protected]").exists()
Solution 5 - Python
For SQL Server, I had to do this:
from sqlalchemy.sql.expression import literal
result = session.query(literal(True)).filter(
session.query(User)
.filter_by(email='...')
.exists()
).scalar()
print(result is not None)
# Resulting query:
# SELECT 1
# WHERE EXISTS (SELECT 1
# FROM User
# WHERE User.email = '...')
But it's much simpler without EXISTS:
result = (
session.query(literal(True))
.filter(User.email == '...')
.first()
)
print(result is not None)
# Resulting query:
# SELECT TOP 1 1
# FROM User
# WHERE User.email = '...'
Solution 6 - Python
it can be done:
from sqlalchemy import select
user = session.scalars(
select(User).where(User.email=="[email protected]")
).first()
if user:
pass
else:
pass