类型错误：only() 需要 2 个位置参数，但给出了 3 个

Question

Here I am trying to get only two fields from cassandra using only() but when I am passing field names it's giving me above error, I have also tried passing self but did't work. After getting those two fields I need to convert them in two arrays so that I can plot the graph with names and marks.

Here is the code:

from flask import *
from flask_cqlalchemy import CQLAlchemy

app = Flask(__name__)
app.config['CASSANDRA_HOSTS'] = ['127.0.0.1']
app.config['CASSANDRA_KEYSPACE'] = "emp"

db = CQLAlchemy(app)

class Student(db.Model):
    uid = db.columns.Integer(primary_key=True)
    marks = db.columns.Integer(primary_key=True)
    username = db.columns.Text(required=True)
    password = db.columns.Text()

    @app.route('/meriting')
    def show_meritlist():
        ob = Student.objects().filter().only(Student.marks, Student.username)
        ob = ob.filter(Student.marks >= 65).allow_filtering()
        return render_template('merit.html', ml = ob)

db.sync_db()
if __name__ == '__main__':
    app.run(debug = True)

Answer 1

only() takes only one parameter that should be an iterable. Try:

ob = Student.objects().filter().only((Student.marks, Student.username))