Flask组件之Flask-session

1、Flask模块中session与Flask-session组件中session的继承关系：

　　Flask模块sessions.py：

class SessionInterface(object):
    def open_session(self, app, request):
        raise NotImplementedError()

    def save_session(self, app, session, response):
        raise NotImplementedError()

class SecureCookieSessionInterface(SessionInterface):
    def open_session(self, app, request):
        pass

    def save_session(self, app, session, response):
        pass

　　flask-session组件sessions.py:

class SessionInterface(FlaskSessionInterface):
    pass

class NullSessionInterface(SessionInterface):
    pass
    
class RedisSessionInterface(SessionInterface):
    pass
    
class MemcachedSessionInterface(SessionInterface):
    pass
    
class FileSystemSessionInterface(SessionInterface):
    pass
    
class MongoDBSessionInterface(SessionInterface):
    pass
    
class SqlAlchemySessionInterface(SessionInterface):
    pass

2、Flask-session在Flask项目中的使用

2.1、从Flask-session导入Session

flask_session import Session

2.2、配置参数

app.config['SESSION_TYPE'] = 'redis'
# app.config['SESSION_TYPE'] = 'filesystem'
app.config['SESSION_REDIS'] = redis.Redis(host='140.143.227.206',port=6379,password='1234')

2.3、实例化Session

Session(app)

　　实例化Session，根据配置的SESSION_TYPE类型实例化不同类型的SessionInterface，并将结果赋值给app.session_interface。

　　Session类源码：

class Session(object):
    """This class is used to add Server-side Session to one or more Flask
    applications.

    There are two usage modes.  One is initialize the instance with a very
    specific Flask application::

        app = Flask(__name__)
        Session(app)

    The second possibility is to create the object once and configure the
    application later::

        sess = Session()

        def create_app():
            app = Flask(__name__)
            sess.init_app(app)
            return app

    By default Flask-Session will use :class:`NullSessionInterface`, you
    really should configurate your app to use a different SessionInterface.

    .. note::

        You can not use ``Session`` instance directly, what ``Session`` does
        is just change the :attr:`~flask.Flask.session_interface` attribute on
        your Flask applications.
    """

    def __init__(self, app=None):
        self.app = app
        if app is not None:
            self.init_app(app)

    def init_app(self, app):
        """This is used to set up session for your app object.

        :param app: the Flask app object with proper configuration.
        """
        app.session_interface = self._get_interface(app)

    def _get_interface(self, app):
        config = app.config.copy()
        # 如果SESSION_TYPE为空，设置SESSION_TYPE为空
        config.setdefault('SESSION_TYPE', 'null')
        # 如果SESSION_PERMANENT为空，设置为永久的
        config.setdefault('SESSION_PERMANENT', True)
        config.setdefault('SESSION_USE_SIGNER', False)
        # 如果SESSION_KEY_PREFIX为空，设置为key的前缀为session:
        config.setdefault('SESSION_KEY_PREFIX', 'session:')
        # 如果SESSION_REDIS为空，设置redis的连接为None
        config.setdefault('SESSION_REDIS', None)
        # 如果SESSION_MEMCACHED为空，设置memcached的连接为None
        config.setdefault('SESSION_MEMCACHED', None)
        # 如果SESSION_FILE_DIR为空，设置session的存储目录为当前目录flask_session文件夹
        config.setdefault('SESSION_FILE_DIR',
                          os.path.join(os.getcwd(), 'flask_session'))
        # 如果SESSION_FILE_THRESHOLD为空，设置文件阈值为500
        config.setdefault('SESSION_FILE_THRESHOLD', 500)
        # 如果SESSION_FILE_MODE为空，设置文件模式为384
        config.setdefault('SESSION_FILE_MODE', 384)
        # 如果SESSION_MONGODB为空，设置mongodb的连接为None
        config.setdefault('SESSION_MONGODB', None)
        # 如果SESSION_MONGODB_DB为空，设置存储session的mongodb数据库为flask_session
        config.setdefault('SESSION_MONGODB_DB', 'flask_session')
        # 如果SESSION_MONGODB_COLLECT为空，设置存储session的mongodb的表名为sessions
        config.setdefault('SESSION_MONGODB_COLLECT', 'sessions')
        # 如果SESSION_SQLALCHEMY为空，设置SQLALCHEMY的连接为None
        config.setdefault('SESSION_SQLALCHEMY', None)
        # 如果SESSION_SQLALCHEMY_TABLE为空，设置SQLALCHEMY的表名为sessions
        config.setdefault('SESSION_SQLALCHEMY_TABLE', 'sessions')

        # session存储在redis
        if config['SESSION_TYPE'] == 'redis':
            # 实例化redis session接口
            session_interface = RedisSessionInterface(
                config['SESSION_REDIS'], config['SESSION_KEY_PREFIX'],
                config['SESSION_USE_SIGNER'], config['SESSION_PERMANENT'])
        # session存储在memcached
        elif config['SESSION_TYPE'] == 'memcached':
            session_interface = MemcachedSessionInterface(
                config['SESSION_MEMCACHED'], config['SESSION_KEY_PREFIX'],
                config['SESSION_USE_SIGNER'], config['SESSION_PERMANENT'])
        # session存储在filesystem
        elif config['SESSION_TYPE'] == 'filesystem':
            session_interface = FileSystemSessionInterface(
                config['SESSION_FILE_DIR'], config['SESSION_FILE_THRESHOLD'],
                config['SESSION_FILE_MODE'], config['SESSION_KEY_PREFIX'],
                config['SESSION_USE_SIGNER'], config['SESSION_PERMANENT'])
        # session存储在mongodb
        elif config['SESSION_TYPE'] == 'mongodb':
            session_interface = MongoDBSessionInterface(
                config['SESSION_MONGODB'], config['SESSION_MONGODB_DB'],
                config['SESSION_MONGODB_COLLECT'],
                config['SESSION_KEY_PREFIX'], config['SESSION_USE_SIGNER'],
                config['SESSION_PERMANENT'])
        # session存储在sqlalchemy
        elif config['SESSION_TYPE'] == 'sqlalchemy':
            session_interface = SqlAlchemySessionInterface(
                app, config['SESSION_SQLALCHEMY'],
                config['SESSION_SQLALCHEMY_TABLE'],
                config['SESSION_KEY_PREFIX'], config['SESSION_USE_SIGNER'],
                config['SESSION_PERMANENT'])
        # 不使用session
        else:
            session_interface = NullSessionInterface()

        return session_interface

2.4、Flask-session支持的session存储方式

存储方式	session操作接口类
redis	RedisSessionInterface
memcached	MemcachedSessionInterface
filesystem	FileSystemSessionInterface
mongodb	MongoDBSessionInterface
sqlalchemy	SqlAlchemySessionInterface