Sqlalchemy query/filter to check for duplicates on INSERT Python

Question

I have a database of participants in a c

# ORM
class_students = db.Table(
    'class_students',
    db.Column('class_id', db.Integer(), db.ForeignKey('class.id')),
    db.Column('user_id', db.Integer(), db.ForeignKey('users.id')),
)

class Class(db.Model):
 id = db.Column(db.Integer)
 name=db.Column(db.String())

 students = db.relationship('User', secondary=class_students,
                            backref=db.backref('classes', lazy='dynamic'))

class User(db.Model):
 id = db.Column(db.Integer)
 username=db.Column(db.String())

Example

When creating a class, I would immediately add students to it, like this:

students_ids = [900,700,40]

new_class = Class()
db.session.add(new_class)
db.session.commit()

for id in students_ids:
    new_class.students.append(id)

The above is working fine but now I want to avoid duplicates when inserting students in a new class:

How do i check if this selected students are already in that Class?

Answer 1

Hi you can check if a student row exists in your db like this

exists = db.session.query(Student.id).filter_by(name=name).scalar() is not None

So you can check if the student exists by name or something. You can just replace name with your variable