完成评论功能

1. 定义评论的视图函数
   @app.route('/comment/',methods=['POST'])
   def comment()：
   读取前端页面数据，保存到数据库中
2. 用<input type="hidden" 方法获取前端的"question_id" 
3. 显示评论次数
4. 要求评论前登录
5. 尝试实现详情页面下的评论列表显示

   from flask import Flask, render_template, request, redirect, url_for, session
   from flask_sqlalchemy import SQLAlchemy
   import config
   from functools import wraps
   from datetime import datetime
   
   app = Flask(__name__)
   app.config.from_object(config)
   db = SQLAlchemy(app)
   
   
   class User(db.Model):
       __tablename__ = 'user'
       id = db.Column(db.Integer, primary_key=True, autoincrement=True)
       username = db.Column(db.String(20), nullable=False)
       password = db.Column(db.String(20), nullable=False)
   
   
   class Question(db.Model):
       __tablename__ = 'question'
       id = db.Column(db.Integer, primary_key=True, autoincrement=True)
       title = db.Column(db.String(100), nullable=False)
       detail = db.Column(db.Text, nullable=False)
       creat_time = db.Column(db.DateTime, default=datetime.now)
       author_id = db.Column(db.Integer, db.ForeignKey('user.id'))
       author = db.relationship('User', backref=db.backref('question'))
   
   class Comment(db.Model):
       __tablename__ = 'comment'
       id = db.Column(db.Integer, primary_key=True, autoincrement=True)
       author_id = db.Column(db.Integer, db.ForeignKey('user.id'))
       question_id = db.Column(db.Integer, db.ForeignKey('question.id'))
       creat_time=db.Column(db.DateTime, default=datetime.now)
       detail=db.Column(db.Text,nullable=False)
       question=db.relationship('Question',backref=db.backref('comments'))
       author=db.relationship('User',backref=db.backref('comments'))
   
   
   db.create_all()
   
   
   @app.route('/')
   def daohang():
       context={
           'questions':Question.query.order_by('creat_time').all()
       }
       return render_template('index.html',**context)
   
   @app.route('/detail/<question_id>',methods=['GET','POST'])
   def detail(question_id):
       quest=Question.query.filter(Question.id == question_id).first()
       return render_template('detail.html',ques=quest)
   
   
   def loginFirst(func):
       @wraps(func)
       def wrapper(*args, **kwargs):
           if session.get('user'):
               return func(*args, **kwargs)
           else:
               return redirect(url_for('login'))
       return wrapper
   
   @app.route('/comment/',methods=['POST'])
   @loginFirst
   def comment():
       comment=request.form.get('new_comment')
       ques_id=request.form.get('question_id')
       auth_id=User.query.filter(User.username==session.get('user')).first().id
       comm=Comment(author_id=auth_id,question_id=ques_id,detail=comment)
       db.session.add(comm)
       db.session.commit()
       return redirect(url_for('detail',question_id=ques_id))
   
   
   
   
   @app.route('/login/', methods=['GET', 'POST'])
   def login():
       if request.method == 'GET':
           return render_template('login.html')
       else:
           username = request.form.get('username')
           password = request.form.get('password')
           user = User.query.filter(User.username == username, User.password == password).first()
           if user:
               session['user'] = username
               session.permanent = True
               return redirect(url_for('daohang'))
           else:
               return 'error username or password'
   
   
   
   @app.context_processor
   def mycontext():
       usern = session.get('user')
       if usern:
           return {'username': usern}
       else:
           return {}
   
   
   @app.route('/logout/')
   def logout():
       session.clear()
       return redirect(url_for('regist'))
   
   
   @app.route('/regist/', methods=['GET', 'POST'])
   def regist():
       if request.method == 'GET':
           return render_template('regist.html')
       else:
           username = request.form.get('username')
           password = request.form.get('password')
           user = User.query.filter(User.username == username).first()
           if user:
               return 'username existed'
           else:
               user = User(username=username, password=password)
               db.session.add(user)
               db.session.commit()
               return redirect(url_for('login'))
   
   
   
   
   
   @app.route('/question/', methods=['GET', 'POST'])
   @loginFirst
   def question():
       if request.method == 'GET':
           return render_template('question.html')
       else:
           title = request.form.get('title')
           detail = request.form.get('detail')
           author_id = User.query.filter(User.username == session.get('user')).first().id
           question = Question(title=title, detail=detail, author_id=author_id)
           db.session.add(question)
           db.session.commit()
           return redirect(url_for('daohang'))
   
   if __name__ == '__main__':
       app.run(debug=True)

   {% extends 'daohang.html' %}
   {% block title %}问答详情{% endblock %}
   
   {% block main %}
       <div class="page-header">
           <h3>Title {{ ques.title }}<br><small>{{ ques.author.username }} <span class="badge">{{ ques.creat_time }}</span></small>></h3>
       </div>
       <p class="lead">detail{{ ques.detail }}</p>
       <hr>
   
       <form action="{{ url_for('comment') }}"method="post" style="...">
           <div class="form-group">
               <textarea name="new_comment" id="new-comment" class="form-control" rows="3"
                         placeholder="write your comment"></textarea>
               <input type="hidden" name="question_id" value="{{ ques.id }}">
           </div>
           <button type="submit" class="btn btn-default">发送</button>
       </form>
       <h4>评论:({{ ques.comments|length }})</h4>>
       <ul class="list-group" style="margin:10px"></ul>>
   {% endblock %}