user_following_id = Column("user_following_id", Integer(), nullable=False, unique=True, default=None, primary_key=True)

    user_id = Column("user_id", Integer(), ForeignKey('users.user_id'), nullable=False, unique=None, default=None)

    follows_repo_id = Column("follows_repository_id", Integer(), ForeignKey('repositories.repo_id'), nullable=True, unique=None, default=None)

    follows_user_id = Column("follows_user_id", Integer(), ForeignKey('users.user_id'), nullable=True, unique=None, default=None)

    follows_from = Column('follows_from', DateTime(timezone=False), nullable=True, unique=None, default=datetime.datetime.now)

    user = relationship('User', primaryjoin='User.user_id==UserFollowing.user_id')

    follows_user = relationship('User', primaryjoin='User.user_id==UserFollowing.follows_user_id')

    follows_repository = relationship('Repository', order_by='Repository.repo_name')

    @classmethod

    def get_repo_followers(cls, repo_id):

        return cls.query().filter(cls.follows_repo_id == repo_id)

class CacheInvalidation(Base, BaseModel):

    __tablename__ = 'cache_invalidation'

    __table_args__ = (

        UniqueConstraint('cache_key'),

        Index('key_idx', 'cache_key'),

        {'extend_existing': True, 'mysql_engine': 'InnoDB',

         'mysql_charset': 'utf8'},

    )

    # cache_id, not used

    cache_id = Column("cache_id", Integer(), nullable=False, unique=True, default=None, primary_key=True)

    # cache_key as created by _get_cache_key

    cache_key = Column("cache_key", String(255, convert_unicode=False, assert_unicode=None), nullable=True, unique=None, default=None)

    # cache_args is a repo_name

    cache_args = Column("cache_args", String(255, convert_unicode=False, assert_unicode=None), nullable=True, unique=None, default=None)

    # instance sets cache_active True when it is caching,

    # other instances set cache_active to False to indicate that this cache is invalid

    cache_active = Column("cache_active", Boolean(), nullable=True, unique=None, default=False)

    def __init__(self, cache_key, repo_name=''):

        self.cache_key = cache_key

        self.cache_args = repo_name

        self.cache_active = False

    def __unicode__(self):

        return u"<%s('%s:%s')>" % (self.__class__.__name__,

                                  self.cache_id, self.cache_key)

    def get_prefix(self):

        """

        Guess prefix that might have been used in _get_cache_key to generate self.cache_key .

        Only used for informational purposes in repo_edit.html .

        """

    @classmethod

    def _get_cache_key(cls, key):

        """

        Wrapper for generating a unique cache key for this instance and "key".

        key must / will start with a repo_name which will be stored in .cache_args .

        """

        import rhodecode

        prefix = rhodecode.CONFIG.get('instance_id', '')

        return "%s%s" % (prefix, key)

    @classmethod

    def _get_or_create_inv_obj(cls, key, repo_name):

        inv_obj = Session().query(cls).filter(cls.cache_key == key).scalar()

        if not inv_obj:

            try:

                inv_obj = CacheInvalidation(key, repo_name)

                Session().add(inv_obj)

                Session().commit()

            except Exception:

                log.error(traceback.format_exc())

                Session().rollback()

        return inv_obj

    @classmethod

    def invalidate(cls, key):

        """

        Returns Invalidation object if the local cache with the given key is invalid,

        None otherwise.

        """

        repo_name = key

        repo_name = remove_suffix(repo_name, '_README')

        repo_name = remove_suffix(repo_name, '_RSS')

        repo_name = remove_suffix(repo_name, '_ATOM')

        cache_key = cls._get_cache_key(key)

        inv_obj = cls._get_or_create_inv_obj(cache_key, repo_name)

        if inv_obj and not inv_obj.cache_active:

            # `cache_active = False` means that this cache

            # no longer is valid

            return inv_obj

    @classmethod

    def set_invalidate(cls, key=None, repo_name=None):

        """

        Mark this Cache key for invalidation, either by key or whole

        cache sets based on repo_name