key = (repo_name + '_' + kind) if kind else repo_name

        cache_key = cls._get_cache_key(key)

        if valid_cache_keys and cache_key in valid_cache_keys:

            return True

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

        if not inv_obj:

            inv_obj = CacheInvalidation(cache_key, repo_name)

        if inv_obj.cache_active:

            return True

        inv_obj.cache_active = True

        Session().add(inv_obj)

        Session().commit()

        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'),

        Index('cc_pull_request_id_idx', 'pull_request_id'),

        {'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')

    repo = relationship('Repository')

    # status_change is frequently used directly in templates - make it a lazy

    # join to avoid fetching each related ChangesetStatus on demand.

    # There will only be one ChangesetStatus referencing each comment so the join will not explode.

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

    pull_request = relationship('PullRequest')

    @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 is not None:

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

        elif pull_request_id is not None:

            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'),

        Index('cs_pull_request_id_idx', 'pull_request_id'),

        Index('cs_changeset_comment_id_idx', 'changeset_comment_id'),

        Index('cs_pull_request_id_user_id_version_idx', 'pull_request_id', 'user_id', '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")),

    ]

    author = relationship('User')

    repo = relationship('Repository')

    comment = relationship('ChangesetComment')

    pull_request = relationship('PullRequest')

    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__ = (

        Index('pr_org_repo_id_idx', 'org_repo_id'),

        Index('pr_other_repo_id_idx', 'other_repo_id'),

        {'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(255), nullable=True)

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

    status = Column('status', Unicode(255), 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(255), nullable=False)

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

    other_ref = Column('other_ref', Unicode(255), nullable=False)

    @hybrid_property

    def revisions(self):

        return self._revisions.split(':')

    @revisions.setter

    def revisions(self, val):

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

    @property

    def org_ref_parts(self):

        return self.org_ref.split(':')

    @property

    def other_ref_parts(self):

        return self.other_ref.split(':')

    author = relationship('User')

    reviewers = relationship('PullRequestReviewers',

                             cascade="all, delete-orphan")

    org_repo = relationship('Repository', primaryjoin='PullRequest.org_repo_id==Repository.repo_id')

    other_repo = relationship('Repository', primaryjoin='PullRequest.other_repo_id==Repository.repo_id')

    statuses = relationship('ChangesetStatus')

    comments = relationship('ChangesetComment',

                             cascade="all, delete-orphan")

    def is_closed(self):

        return self.status == self.STATUS_CLOSED

    @property

    def last_review_status(self):

        return str(self.statuses[-1].status) if self.statuses else ''

    def user_review_status(self, user_id):

        """Return the user's latest status votes on PR"""

        # note: no filtering on repo - that would be redundant

        status = ChangesetStatus.query()\

            .filter(ChangesetStatus.pull_request == self)\

            .filter(ChangesetStatus.user_id == user_id)\

            .order_by(ChangesetStatus.version)\

            .first()

        return str(status.status) if status else ''

    def __json__(self):

        return dict(

            revisions=self.revisions

        )

    def url(self, **kwargs):

        canonical = kwargs.pop('canonical', None)