return True

        inv_obj.cache_active = True

        Session().add(inv_obj)

        try:

            Session().commit()

        except sqlalchemy.exc.IntegrityError:

            log.error('commit of CacheInvalidation failed - retrying')

            Session().rollback()

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

            if inv_obj is None:

                log.error('failed to create CacheInvalidation entry')

                # TODO: fail badly?

            # else: TOCTOU - another thread added the key at the same time; no further action required

        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'),

        _table_args_default_dict,

    )

    comment_id = Column(Integer(), unique=True, primary_key=True)

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

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

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

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

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

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

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

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

    modified_at = Column(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()

    def url(self):

        anchor = "comment-%s" % self.comment_id

        import kallithea.lib.helpers as h

        if self.revision:

            return h.url('changeset_home', repo_name=self.repo.repo_name, revision=self.revision, anchor=anchor)

        elif self.pull_request_id is not None:

            return self.pull_request.url(anchor=anchor)

    def deletable(self):

        return self.created_on > datetime.datetime.now() - datetime.timedelta(minutes=5)

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'),

        Index('cs_repo_id_pull_request_id_idx', 'repo_id', 'pull_request_id'),

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

        _table_args_default_dict,

    )

    STATUS_NOT_REVIEWED = DEFAULT = 'not_reviewed'

    STATUS_APPROVED = 'approved'

    STATUS_UNDER_REVIEW = 'under_review'

    STATUSES = [

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

        (STATUS_APPROVED, _("Approved")),

        (STATUS_UNDER_REVIEW, _("Under review")),

    ]

    STATUSES_DICT = dict(STATUSES)

    changeset_status_id = Column(Integer(), unique=True, primary_key=True)

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

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

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

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

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

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

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

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

    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 cls.STATUSES_DICT.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'),

        _table_args_default_dict,

    )

    # values for .status

    STATUS_NEW = u'new'

    STATUS_CLOSED = u'closed'

    pull_request_id = Column(Integer(), unique=True, primary_key=True)

    title = Column(Unicode(255), nullable=False)

    description = Column(UnicodeText(10240), nullable=False)

    status = Column(Unicode(255), nullable=False, default=STATUS_NEW) # only for closedness, not approve/reject/etc

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

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

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

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

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

    org_ref = Column(Unicode(255), nullable=False)

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

    other_ref = Column(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(':')

    owner = 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', order_by='ChangesetStatus.changeset_status_id')

    comments = relationship('ChangesetComment', order_by='ChangesetComment.comment_id',

                             cascade="all, delete-orphan")

    def get_reviewer_users(self):

        """Like .reviewers, but actually returning the users"""

        return User.query() \

            .join(PullRequestReviewers) \

            .filter(PullRequestReviewers.pull_request == self) \

            .order_by(PullRequestReviewers.pull_requests_reviewers_id) \

            .all()

    def is_closed(self):

        return self.status == self.STATUS_CLOSED

    def user_review_status(self, user_id):