非类型的Python SQLAlchemy检查

Question

我正在编写一个处理用户注册的python脚本，我需要检查现有用户的SQLAlchemy数据库，但是当lookup.username为非类型时，它会返回一个属性错误。在SQLAlchemy for Flask中是否有检查不存在的条目并通过它的方法

lookup = User.query.filter_by(phonenumber = request.form['number']).first()
            if request.form['username'] == lookup.username:
                return render_template('numberusererror.html', number = request.form['number'], username = request.form['username'])
            elif request.form['number'] != lookup.phonenumber:
                return render_template('numberusererror.html', number = request.form['number'], username = request.form['username'])

Answer 1

在尝试访问查询的属性之前，可以检查查询是否实际返回任何结果

lookup = User.query.filter_by(phonenumber = request.form['number']).first()
if not lookup:
    #return something for non-existent user
    pass
# continue with your code here 
...