Difference between filter and filter_by in SQLAlchemy

Pinpointing the RIGHT query choice

filter allows sophisticated, flexible AND/OR conditions, easily handling SQL functions and complex operations which filter_by can't do:

# When you can't decide who is your favourite user... ed or wendy 🤔
from sqlalchemy import or_
session.query(User).filter(or_(User.name == 'ed', User.name == 'wendy'))


On the flip side, filter_by excels in its cleaner, more readable syntax for straight-on queries, where just equality checks are needed and no fancy SQL is in sight:

# Let's find every 30-year-old John. It's amazing how popular that name is. 🤷
session.query(MyModel).filter_by(age=30, name='John')


Gaining upper hand with filter's flexibility

filter is your answer for dynamic query needs. It rises to the occasion when queries need to be built dynamically based on various conditions:

# The thrill of the hunt... for the ideal query 🧐
query = session.query(MyModel)
if condition1:
    query = query.filter(MyModel.age > 30)
if condition2:
    query = query.filter(MyModel.name.startswith('A'))
results = query.all()


filter_by cannot match this flexibility, being bound by statically defined keyword arguments.

The BEST of both worlds: Unifying filter and filter_by

Who says you can't have your cake and eat it! Use both filter and filter_by in unison to benefit their individual strengths:

# Filter's the left brain, filter_by's the right. Together they're... the 'perfect query' brain!
from sqlalchemy import or_
session.query(MyModel).filter_by(name='John').filter(or_(MyModel.age > 20, MyModel.education == 'PhD'))


Making the most from object retrieval: Using get

To gain performance boosts, use get when fetching objects by primary key. It taps into session's identity map, returning the object without needing a new query if it already exists in the map:

# The fastest gun in the ORM? Yep, it's '.get()'
my_model = session.query(MyModel).get(primary_key)


In this context, the identity map also plays an ally to filter_by, offering potential cache hits for results already in the session.

Leveling up with OR conditions in filter

Navigating OR conditions is easier with filter. Use the bitwise OR | operator or or_() function from sqlalchemy:

# Ed or anyone younger than 5. Fascinating group that'd be, huh? 🤣
from sqlalchemy import or_
session.query(User).filter(or_(User.name == 'ed', User.age < 5))


And the alternative using bitwise OR:

session.query(User).filter((User.name == 'ed') | (User.age < 5))


The syntax showdown: filter vs filter_by

Understanding their syntax difference helps nail the right choice:

• filter: involves expressions like column == expression

session.query(MyModel).filter(MyModel.age == 30)


• filter_by: operates with keyword arguments equating to values

# A bit like: Alexa, find me the models with age 30." 🗣️🎙️
session.query(MyModel).filter_by(age=30)


Seize the syntax divergence between them to inform your efficient and sophisticated query formulations.