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. 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):
    __tablename__ = 'user'
    id = db.Column(db.Integer, primary_key=TabError, autoincrement=True)
    username = db.Column(db.String(20), nullable=False)
    password = db.Column(db.String(20), nullable=False)
    # nickname = db.Column(db.String(20))


# 查询删除
# user = User.query.filter(User.username == 'lin').first()
# db.session.delete(user)
# db.session.commit()

# 修改
# user = User.query.filter(User.username == 'lin').first()
# user.password = '1234'
# print(user.username,user.password)
# db.session.commit()

# 增加
# user = User(username = 'lin',password = 'lin')
# db.session.add(user)
# db.session.commit()

db.create_all()


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


@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:
            session['user'] = username
            session.permanent = True
            return redirect(url_for('jianshu'))
        else:
            return 'error username or password'


@app.route("/enroll/", methods=['GET', 'POST'])
def enroll():
    if request.method == 'GET':
        return render_template('enroll.html')
    else:
        username = request.form.get('username')
        password = request.form.get('password')
        user = User.query.filter(User.username == username).first()
        if user:
            return 'username exited'
        else:
            user = User(username=username, password=password)
            db.session.add(user)
            db.session.commit()
            return redirect(url_for('login'))


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


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