如何在flask中使用after_request关闭数据库连接和python？

处理请求后,如何使用after_request装饰器关闭连接？我使用before_request打开每个api请求的连接,如下所示：
使用sqlalchemy core 1.0.8和Postgresql 9.5：

#engine = create_engine(os.environ.get("DB_URL"))
DB_URL="postgresql://mowner:passwd@localhost/mydb"

@app.before_request
def before_request():
    engine = create_engine(DB_URL, strategy='threadlocal')
    conn = engine.connect()


@app.after_request
def after_request(conn):
     if conn is not None:
         print 'closing connection'
         conn.close()

示例api调用：

@app.route('/api/v1.0/categories', methods=['GET'])
def categories_list():
    '''
    Return categories list
    '''
    if 'id' in session:
        categories_list = []
        s = select([categories])
        rs = conn.execute(s)
        if rs.rowcount > 0:
            for r in rs:
                categories_list.append(dict(r))
            rs.close()
        # print 'this doesnt execute'
        return jsonify({'categories list': categories_list}), 200

    return jsonify({'message': "UNAUTHORIZED"}), 401

视图是api调用,仅返回对象列表,已添加或编辑对象和消息.如何准确地将连接对象传递给after_request装饰器？我真的不能遵循文档
确切的代码将对我有所帮助.

解决方法:

您可以使用flask.g来引用创建全局db连接对象并在任何地方使用它

from flask import Flask, g

#engine = create_engine(os.environ.get("DB_URL"))
DB_URL="postgresql://mowner:passwd@localhost/mydb"

@app.before_request
def before_request():
   engine = create_engine(DB_URL, strategy='threadlocal')
   conn = engine.connect()
   g.db = conn

然后像这样在您的路线中使用连接

@app.route('/api/v1.0/categories', methods=['GET'])
def categories_list():
    '''
    Return categories list
    '''
    if 'id' in session:
        categories_list = []
        s = select([categories])
        rs = g.db.execute(s) # change in variable
        if rs.rowcount > 0:
           for r in rs:
             categories_list.append(dict(r))
        rs.close()
        # print 'this doesnt execute'
       return jsonify({'categories list': categories_list}), 200
    return jsonify({'message': "UNAUTHORIZED"}), 401

然后最后像这样关闭它：

@app.after_request
def after_request(response):
    if g.db is not None:
        print 'closing connection'
        g.db.close()
     return response