完成登录功能，用session记住用户名

登录功能完成：

js:设置return
html:设置
1. form
2. input
3. ```
οnclick="return fnLogin()"
```
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：

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

JS：

function myLogin() {
    var oUname=document.getElementById("uname");
    var oPass=document.getElementById("upass");
    var oError=document.getElementById("error_box");
    oError.innerHTML="<br>";
    //username
    if(oUname.value.length<6||oUname.value.length>20){
        oError.innerHTML="username must be 6-20.";
        return false;
    }else if((oUname.value.charCodeAt(0)>=48)&&(oUname.value.charCodeAt(0)<=57)){
        oError.innerHTML="firt name can't numbuter.";
        return false;
    }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="only number and letter";
            return false;
        }
    }
    if(oPass.value.length<6||oPass.value.length>20){
        oError.innerHTML="password must be 6-20.";
        return false;
    }
    return true;
    // window.alert("Login Successful")
    }

html：

{% extends'base.html' %}
{% block title %}
    Login
{% endblock %}
{% block head %}
    <script src="{{ url_for('static',filename='js/denglu1.js') }}"></script>
    <link rel="stylesheet" href="{{ url_for('static',filename='css/denglu1.css')}}">
{% endblock %}
{% block main %}
<body>
  <div class="login">
    <h1>Login</h1>
    <form class="form" method="post" action="{{ url_for('sign_in') }}">
      <p class="field">
        <input id="uname" type="text" name="username" placeholder="Username" required/>
        <i class="fa fa-user"><img src="../static/images/daohang1.jpg" width="44px" height="auto"></i>
      </p>
      <p class="field">
        <input id="upass" type="password" name="password" placeholder="Password" required/>
        <i class="fa fa-lock"><img src="../static/images/daohang1.jpg" width="44px" height="auto"></i>
      </p>
         <button class="button" onclick="return myLogin()">Login</button>

        <div id="error_box"><br></div>
    </form>
  </div>
</body>
{% endblock %}
</html>

py：

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)
#db.create_all()

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

@app.route('/sign_in/',methods=['GET','POST'])
def sign_in():
    if request.method == 'GET':
        return render_template('denglu1.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
                session.permanent = True
                return redirect(url_for('home'))
            else:
                return 'password error'
        else:
            return 'username is not existed.'


@app.route('/sign_up/',methods=['GET','POST'])
def sign_up():
    if request.method == 'GET':
        return render_template('zhuce.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:
            user1 = User(username=username, password=password)
            db.session.add(user1)
            db.session.commit()
            return redirect(url_for('sign_in'))


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

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

session：

import os
SECRET_KEY = os.urandom(24)

SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://root:@localhost:3306/zhuce?charset=utf8'
SQLALCHEMY_TRACK_MODIFICATIONS = False

完成登录功能，用session记住用户名