if valid_cache_keys and cache_key in valid_cache_keys:

            return True

        try:

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

            if not inv_obj:

                inv_obj = CacheInvalidation(cache_key, repo_name)

            was_valid = inv_obj.cache_active

            inv_obj.cache_active = True

            Session().add(inv_obj)

            Session().commit()

            return was_valid

        except Exception:

            log.error(traceback.format_exc())

            Session().rollback()

            return False

    @classmethod

    def get_valid_cache_keys(cls):

        """

        Return opaque object with information of which caches still are valid

        and can be used without checking for invalidation.

        """

        return set(inv_obj.cache_key for inv_obj in cls.query().filter(cls.cache_active).all())

class ChangesetComment(Base, BaseModel):

    __tablename__ = 'changeset_comments'

    __table_args__ = (

        Index('cc_revision_idx', 'revision'),

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

         'mysql_charset': 'utf8', 'sqlite_autoincrement': True},

    )

    comment_id = Column('comment_id', Integer(), nullable=False, primary_key=True)

    repo_id = Column('repo_id', Integer(), ForeignKey('repositories.repo_id'), nullable=False)

    revision = Column('revision', String(40), nullable=True)

    pull_request_id = Column("pull_request_id", Integer(), ForeignKey('pull_requests.pull_request_id'), nullable=True)

    line_no = Column('line_no', Unicode(10), nullable=True)

    hl_lines = Column('hl_lines', Unicode(512), nullable=True)

    f_path = Column('f_path', Unicode(1000), nullable=True)

    user_id = Column('user_id', Integer(), ForeignKey('users.user_id'), nullable=False)

    text = Column('text', UnicodeText(25000), nullable=False)

    created_on = Column('created_on', DateTime(timezone=False), nullable=False, default=datetime.datetime.now)

    modified_at = Column('modified_at', DateTime(timezone=False), nullable=False, default=datetime.datetime.now)

    author = relationship('User', lazy='joined')

    repo = relationship('Repository')

    status_change = relationship('ChangesetStatus', cascade="all, delete, delete-orphan")

    @classmethod

    def get_users(cls, revision=None, pull_request_id=None):

        """

        Returns user associated with this ChangesetComment. ie those

        who actually commented

        :param cls:

        :param revision:

        """

        q = Session().query(User)\

                .join(ChangesetComment.author)

        if revision:

            q = q.filter(cls.revision == revision)

        elif pull_request_id:

            q = q.filter(cls.pull_request_id == pull_request_id)

        return q.all()

class ChangesetStatus(Base, BaseModel):

    __tablename__ = 'changeset_statuses'

    __table_args__ = (

        Index('cs_revision_idx', 'revision'),

        Index('cs_version_idx', 'version'),

        UniqueConstraint('repo_id', 'revision', 'version'),

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

         'mysql_charset': 'utf8', 'sqlite_autoincrement': True}

    )

    STATUS_NOT_REVIEWED = DEFAULT = 'not_reviewed'

    STATUS_APPROVED = 'approved'

    STATUS_REJECTED = 'rejected'

    STATUS_UNDER_REVIEW = 'under_review'

    STATUSES = [

        (STATUS_NOT_REVIEWED, _("Not Reviewed")),  # (no icon) and default

        (STATUS_APPROVED, _("Approved")),

        (STATUS_REJECTED, _("Rejected")),

        (STATUS_UNDER_REVIEW, _("Under Review")),

    ]

    changeset_status_id = Column('changeset_status_id', Integer(), nullable=False, primary_key=True)

    repo_id = Column('repo_id', Integer(), ForeignKey('repositories.repo_id'), nullable=False)

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

    revision = Column('revision', String(40), nullable=False)

    status = Column('status', String(128), nullable=False, default=DEFAULT)

    changeset_comment_id = Column('changeset_comment_id', Integer(), ForeignKey('changeset_comments.comment_id'))

    modified_at = Column('modified_at', DateTime(), nullable=False, default=datetime.datetime.now)

    version = Column('version', Integer(), nullable=False, default=0)

    pull_request_id = Column("pull_request_id", Integer(), ForeignKey('pull_requests.pull_request_id'), nullable=True)

    author = relationship('User', lazy='joined')

    repo = relationship('Repository')

    comment = relationship('ChangesetComment', lazy='joined')

    def __unicode__(self):

        return u"<%s('%s:%s')>" % (

            self.__class__.__name__,

            self.status, self.author

        )

    @classmethod

    def get_status_lbl(cls, value):

        return dict(cls.STATUSES).get(value)

    @property

    def status_lbl(self):

        return ChangesetStatus.get_status_lbl(self.status)

class PullRequest(Base, BaseModel):

    __tablename__ = 'pull_requests'

    __table_args__ = (

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

         'mysql_charset': 'utf8', 'sqlite_autoincrement': True},

    )

    # values for .status

    STATUS_NEW = u'new'

    STATUS_CLOSED = u'closed'

    pull_request_id = Column('pull_request_id', Integer(), nullable=False, primary_key=True)

    title = Column('title', Unicode(256), nullable=True)

    description = Column('description', UnicodeText(10240), nullable=True)

    status = Column('status', Unicode(256), nullable=False, default=STATUS_NEW) # only for closedness, not approve/reject/etc

    created_on = Column('created_on', DateTime(timezone=False), nullable=False, default=datetime.datetime.now)

    updated_on = Column('updated_on', DateTime(timezone=False), nullable=False, default=datetime.datetime.now)

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

    _revisions = Column('revisions', UnicodeText(20500))  # 500 revisions max

    org_repo_id = Column('org_repo_id', Integer(), ForeignKey('repositories.repo_id'), nullable=False)

    org_ref = Column('org_ref', Unicode(256), nullable=False)

    other_repo_id = Column('other_repo_id', Integer(), ForeignKey('repositories.repo_id'), nullable=False)

    other_ref = Column('other_ref', Unicode(256), nullable=False)

    @hybrid_property

    def revisions(self):

        return self._revisions.split(':')

    @revisions.setter

    def revisions(self, val):

        self._revisions = ':'.join(val)