Could anyone explain the difference between filter
and filter_by
functions in SQLAlchemy?
Which one should I be using?
This question is related to
python
sqlalchemy
It is a syntax sugar for faster query writing. Its implementation in pseudocode:
def filter_by(self, **kwargs):
return self.filter(sql.and_(**kwargs))
For AND you can simply write:
session.query(db.users).filter_by(name='Joe', surname='Dodson')
btw
session.query(db.users).filter(or_(db.users.name=='Ryan', db.users.country=='England'))
can be written as
session.query(db.users).filter((db.users.name=='Ryan') | (db.users.country=='England'))
Also you can get object directly by PK via get
method:
Users.query.get(123)
# And even by a composite PK
Users.query.get(123, 321)
When using get
case its important that object can be returned without database request from identity map
which can be used as cache(associated with transaction)
We actually had these merged together originally, i.e. there was a "filter"-like method that accepted *args
and **kwargs
, where you could pass a SQL expression or keyword arguments (or both). I actually find that a lot more convenient, but people were always confused by it, since they're usually still getting over the difference between column == expression
and keyword = expression
. So we split them up.
filter_by
uses keyword arguments, whereas filter
allows pythonic filtering arguments like filter(User.name=="john")
Source: Stackoverflow.com