.label() addition of two columns

[Dani Hodovic]

I know it's possible to label an arbitrary column in a query:

session.query(Person.name.label("name"))

It isn't possible to do this:

session.query((Person.age + Person.wealth).label("sum"))

How would I go about labeling an addition of different columns?

[Dani Hodovic]

Solved it myself with literal_column

session.query(literal_column("col1 + col2").label("lbl"))

[Mike Bayer]

please define "it isn't possible". There's no issue adding two columns and labeling them.

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Person(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    age = Column(Integer)
    wealth = Column(Integer)

e = create_engine("sqlite://")
Base.metadata.create_all(e)

s = Session(e)
s.add(Person(age=5, wealth=10))
s.commit()

row = s.query((Person.age + Person.wealth).label('sum')).first()
print row.sum

output:

15

[Mike Bayer]

using literal_column is the wrong approach here when you have mapped columns to work with directly.

[Dani Hodovic]

Sorry Mike, I was in a rush and got another error which I thought had to do with this... Seems like your approach works perfectly.

What is the use case for literal columns?

[Mike Bayer]

when you want to write some SQL column expression that is not cleanly met by the existing constructs, like a constant, literal_column("'TEXT'").

[Dani Hodovic]

Oh, so syntax that is db specific?

[mohit agrawal]

@zzzeek What if I want to pick the columns to add dynamically from an array ?

[Mike Bayer]

columns[some_index_a] + columns[some_index_b] ?