More specific SQL query with flask-wtf queryselect

I'd like to create a Login-Form using Flask and WTF. The application should read the nicknames of all users out of a database-table and display them in a QuerySelectField.

It does work - but I think that I can do it in a 'nicer way'...

I have a database table like this:

 id | nickname  |    fullname    |          email
----+-----------+----------------+--------------------------
  1 | Admin     | The Admin      | admin@example.com
  2 | JDoe      | John Doe       | jd@example.com

In my models.py I have the corresponding class User and a function getUser:

from app import db

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    nickname = db.Column(db.String(64), index=True, unique=True)
    fullname = db.Column(db.String(64), index=True, unique=True)
    email = db.Column(db.String(120), index=True, unique=True)

    def __repr__(self):
        return '<User %r>' % (self.nickname)

# used for query_factory    
def getUser():
    u = User.query
    return u

The forms.py contains the form-class

from flask.ext.wtf import Form
from wtforms import StringField, BooleanField, SelectField
from wtforms.validators import DataRequired, Required
from wtforms.ext.sqlalchemy.fields import QuerySelectField

from .models import User, getUser

class LoginForm(Form):
    openid = StringField('openid', validators=[DataRequired()])
    remember_me = BooleanField('remember_me', default=False)
    user = QuerySelectField(u'User', query_factory=getUser, get_label='nickname')

As I said, all nicknames appear nicely in my QuerySelectField.

<select id="user" name="user"><option value="1">Admin</option><option value="2">JDoe</option></select>

But I wonder about the query that is made:

INFO sqlalchemy.engine.base.Engine SELECT "user".id AS user_id, "user".nickname AS user_nickname, "user".fullname AS user_fullname, "user".email AS user_email
FROM "user"

It seems whole table is returned and i receive unnecessary Data (fullname and email), too. That's what I want to avoid.

How can I query only User.id and User.nickname and display it in QuerySelectField? (Of course I did research - i tryed filter_by or User.query(User.id, User.nickname) - but only got errors about not matched tuples)

Can anyone help?

Thanks in advance!

mycket

Not sure which version of SQLAlchemy you are using, but as of 0.9.0 there is sqlalchemy.orm.load_only which can be used to easily return a subset of columns for a query.

You could modify getUser() to something like the following:

from functools import partial
from sqlalchemy import orm

def getUser(columns=None):
    u = User.query
    if columns:
        u = u.options(orm.load_only(*columns))
    return u

def getUserFactory(columns=None):
    return partial(getUser, columns=columns)

# subsequently when defining LoginForm
user = QuerySelectField(u'User',
                        query_factory=getUserFactory(['id', 'nickname']),
                        get_label='nickname')