完成登录功能，用session记住用户名

登录功能完成：

1. js:设置return
2. html:设置
   1. form
   2. input

   3. onclick="return fnLogin()"

3. py:
   1. @app.route设置methods
   2. GET
   3. POST
      1. 读取表单数据
      2. 查询数据库
         1. 用户名密码对：
            1. 记住用户名
            2. 跳转到首页
         2. 用户名密码不对：
            1. 提示相应错误。

session：

1. 从`flask`中导入`session`
2. 设置`SECRET_KEY`
3. 操作字典一样操作`session`：增加用户名`session['username']=`username

4. from flask import Flask,render_template,request,redirect,url_for,session
   from flask_sqlalchemy import SQLAlchemy
   import config

   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)
       nickname = db.Column(db.String(50))
   
   
   #db.create_all()
   
   #增加数据
   user=User(username = 'mis1234',password = '111111')
   db.session.add(user)
   db.session.commit()
   
   #查询数据
   user=User.query.filter(user.username == 'mis1234').first()
   print(user.id,user.username,user.password)
   
   
   #修改数据
   user=User.query.filter(user.username == 'mis3333').first()
   user.password = '0000'
   db.session.commit()
   
   #删除数据
   user=User.query.filter(user.username == 'mis3333').first()
   db.session.delete(user)
   db.session.commit()

   @app.route('/')
   def base():
       return render_template('base.html')
   
   
   

   @app.route('/denglu/',methods=['GET','POST'])
   def gg():
       if request.method == 'GET':
           return render_template('denglu.html') #跳转登录
       else:
           usern = request.form.get('username')
           passw = request.form.get('password')
           user = User.query.filter(User.username == usern).first()
           if user:
               if user.password == passw:
                   session['user'] = usern
                   session['user_id'] =user.id
                   session.parmanent = True
                   return redirect(url_for('shouye'))
               else:
                   return u'password error'
           else:
               return u'username is not existed'

   @app.route('/zhuche/', methods=['GET','POST'])
   def login ():
       if request.method =='GET':
           return render_template('zhuce.html')#跳转注册
       else:
           usern = request.form.get('username')
           passw = request.form.get('password')
           nickn = request.form.get('nickname')
           user = User.query.filter(User.username == usern).first()
           if user:
               return u'username existed'
           else:
               user1 = User(username = usern,password = passw,nickname=nickn)
               db.session.add(user1)#数据库操作
               db.session.commit()
               return redirect(url_for('gg'))

   
   
   @app.route('/question/')
   def question():
       return render_template('question.html')
   
   

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

   {% extends 'base.html' %}
   
   {% block denglutitle %}登录{% endblock %}
   
   {% block dengluhead %}
       <link href="../static/css/denglu.css" rel="stylesheet" type="text/css">
       <script src="../static/js/denglu.js"></script>
   {% endblock %}
   
   {% block denglubody %}
       <div class="box">
           <h2>登录</h2>
           <form action="{{ url_for('gg') }}" method="post">
           <div class="input_box">
               username：<input type="text" id="uname" placeholder="请输入用户名" name="username">
           </div>
           <div class="input_box">
               password：<input type="password" id="upass" placeholder="请输入密码" name="password">
           </div>
           <div id="error_box"><br></div>
           <div class="input_box">
               <button onclick="fnLogin()">Enter</button>
           </div>
           </form>
       </div>
   {% endblock %}

   function fnLogin(){
       var oUname = document.getElementById("uname");
       var oUpass = document.getElementById("upass");
       var oError = document.getElementById("error_box");
       var isError=true;
       oError.innerHTML="<br>";
       //uname
       if (oUname.value.length>10 || oUname.value.length < 6){
   
           oError.innerHTML="用户名必须是6-10位！";
           isError=false;
           return isError;
       }else if((oUname.value.charCodeAt(0)>=48)&& (oUname.value.charCodeAt(0))<=57){
           oError.innerHTML="用户名首字母不能是数字！";
           isError=false;
           return isError;
       }else for(var i=0;i<oUname.value.length;i++){
           if((oUname.value.charCodeAt(i)<48 || oUname.value.charCodeAt(i)>57) && (oUname.value.charCodeAt(i)<97 || oUname.value.charCodeAt(i)>122)){
               oError.innerHTML="用户名只能为数字和字母";
               isError=false;
               return isError;
           }
   
   
       }
       //upass
       if(oUpass.value.length>10 || oUpass.value.length<6 ){
           oError.innerHTML="用户密码6-10位！";
           return;
       }
       window.alert("登录成功！")
   }

    config.py

5. #SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:wk21640913@127.0.0.1:3306/mis_1test?charset=utf8'
   import  os
   SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:@127.0.0.1:3306/mis_1?charset=utf8'
   SQLALCHEMY_TRACK_MODIFICATIONS = False
   SECRET_KEY = os.urandom(24)