Get a list of values of one column from the results of a query

Question

I have a User model where users can have the same name. I want to get the email addresses of all the users with a given name. However, I have to do resu

Answer 1

There is a way to return specific columns from a filter_by query using the values method. As follows:

 emails = [r[0] for r in db.session.query(my_table).filter_by(name=name).values('email')]

or:

 emails = [r[0] for r in User.query.filter_by(name=name).values('email')]

values() takes any number of field names as parameters and returns a generator that has tuples with each value from each field name. Using a list comprehension to take the first item of that tuple emails will then be a list of plain string email addresses.

Answer 2

No, there's not really a way around the fact that SQLAlchemy queries return a list of dicts. If you want a specific set of fields, you can query for just those fields, but if you want a list of one field, you'll have to extract it from the result. The following example gets a list of the unique emails for ever user with the given name.

emails = [r.email for r in db.session.query(my_table.c.email).filter_by(name=name).distinct()]

Answer 3

Just to keep a record, I like a wrapper with this function in my common use lib:

def flat_list(l): return ["%s" % v for v in l]

Then:

flat_list(db.session.query(Model.column_attribute).all())