seats = Seat.query.filter_by(invite=None).all()

seats = Seat.query.filter_by(invite!=None).all()

NameError: name 'invite' is not defined

class Seat(db.Model):
    id = db.Column(db.Integer, primary_key=True)

    invite_id = db.Column(db.Integer, db.ForeignKey('invite.id'))
    invite = db.relationship('Invite',
        backref=db.backref('folks', lazy='dynamic'))

seats = Seat.query.filter(Seat.invite != None).all()

seats = Seat.query.filter(Seat.invite_id != None).all()

query.filter(User.name == None)

query.filter(User.name != None)