完成登录功能，用session记住用户名

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

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):
    __table__name = '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()


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

@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')
        nickname=request.form.get('nickname')
        user=User.query.filter(User.username==username).first()
        if user:
            return u'username existed'
        else:
            user=User (username=username,password=password,nickname=nickname)
            db.session.add(user)
            db.session.commit()
            return redirect(url_for('login'))



@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).first()
        if user:
            if user.password==password:
                session['user']=username
                return redirect(url_for('index'))
            else:
                return u'password error'
        else:
            return u'username is not existed'

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

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

import os
SECRET_KEY = os.urandom(24)
SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:123456@localhost:3306/mis_db?charset=utf8'
SQLALCHEMY_TRACK_MODIFICATIONS = False

login.html

{% extends 'base.html' %}

{% block title %}登录{% endblock %}

{% block head %}
    <link href="{{ url_for('static',filename='css/login.css') }}" rel="stylesheet" type="text/css">
    <script src="{{ url_for('static',filename='js/login.js') }}"></script>
{% endblock %}
{% block main %}
<div class="a" >
    <div class="login" ><h2>登录</h2></div>
    <form action="{{ url_for('login') }}"method="post">
    <div class="a1" >
        Username：<input id="name" type="text"placeholder="请输入用户名" name="username"><br>
        Password：<input id="password" type="password"placeholder="请输入密码" name="password"><br>
        </div>
        <div id="error_box"><br></div>
      <div class="a2" >
         <button onclick="myLogin()">登录</button>
         <button type="button" onclick=window.alert("是否取消登录！")>取消</button>
</div>
    </div>
    <div class="a3" >Created.by.xuejing</div>
    </form>
{% endblock %}

login.js

function myLogin(){
            var uName=document.getElementById("name");
            var uError=document.getElementById("error_box");
            var upass = document.getElementById("password");
            var isError=true;
            uError.innerHTML = "<br>"
            //uname
            if(uName.value.length>12 || uName.value.length<6){
                uError.innerHTML="Username 6-12 bits";
                isError=false;
                return isError;
            }else if((uName.value.charCodeAt(0)>=48)&& uName.value.charCodeAt(0)<=57){
                uError.innerHTML="The first letter cannot be numeric";
                isError=false;
                return isError;
            }else for(var i=0; i<uName.value.length;i++){
                if((uName.value.charCodeAt(i)<48 || uName.value.charCodeAt(i)>57)&&(uName.value.charCodeAt(i)<97 || uName.value.charCodeAt(i)>122 )){
                    uError.innerHTML = "only letter or number.";
                    isNotError=false;
                    return isError;
                }
            }


            if(upass.value.length>12 || upass.value.length<6){
                uError.innerHTML="password 6-12 bits";
                isError=false;
                return isError;
            }
            return isError;


        }