backend = get_backend(alias)

        except VCSError:

            log.error(traceback.format_exc())

            log.error('Perhaps this repository is in db and not in '

                      'filesystem run rescan repositories with '

                      '"destroy old data " option from admin panel')

            return

        if alias == 'hg':

            repo = backend(repo_full_path, create=False,

                           baseui=self._ui)

            #skip hidden web repository

            if repo._get_hidden():

                return

        else:

            repo = backend(repo_full_path, create=False)

        return repo

class Group(Base):

    __tablename__ = 'groups'

    __table_args__ = (UniqueConstraint('group_name', 'group_parent_id'),

                      CheckConstraint('group_id != group_parent_id'), {'extend_existing':True},)

    __mapper_args__ = {'order_by':'group_name'}

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

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

    group_parent_id = Column("group_parent_id", Integer(), ForeignKey('groups.group_id'), nullable=True, unique=None, default=None)

    group_description = Column("group_description", String(length=10000, convert_unicode=False, assert_unicode=None), nullable=True, unique=None, default=None)

    parent_group = relationship('Group', remote_side=group_id)

    def __init__(self, group_name='', parent_group=None):

        self.group_name = group_name

        self.parent_group = parent_group

    def __repr__(self):

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

                                  self.group_name)

    @classmethod

    def url_sep(cls):

        return '/'

    @property

    def parents(self):

        groups = []

        if self.parent_group is None:

            return groups

        cur_gr = self.parent_group

        groups.insert(0, cur_gr)

        cnt = 0

        while 1:

            cnt += 1

            gr = getattr(cur_gr, 'parent_group', None)

            cur_gr = cur_gr.parent_group

            if gr is None:

                break

                # this will prevent accidental infinit loops

                log.error('group nested more than %s' %

                break

            groups.insert(0, gr)

        return groups

    @property

    def full_path(self):

        return Group.url_sep().join([g.group_name for g in self.parents] +

                        [self.group_name])

    @property

    def repositories(self):

        return Session.query(Repository).filter(Repository.group == self)

class Permission(Base):

    __tablename__ = 'permissions'

    __table_args__ = {'extend_existing':True}

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

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

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

    def __repr__(self):

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

                                  self.permission_id, self.permission_name)

    @classmethod

    def get_by_key(cls, key):

        return Session.query(cls).filter(cls.permission_name == key).scalar()

class RepoToPerm(Base):

    __tablename__ = 'repo_to_perm'

    __table_args__ = (UniqueConstraint('user_id', 'repository_id'), {'extend_existing':True})

    repo_to_perm_id = Column("repo_to_perm_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)

    permission_id = Column("permission_id", Integer(), ForeignKey('permissions.permission_id'), nullable=False, unique=None, default=None)

    repository_id = Column("repository_id", Integer(), ForeignKey('repositories.repo_id'), nullable=False, unique=None, default=None)

    user = relationship('User')

    permission = relationship('Permission')

    repository = relationship('Repository')

class UserToPerm(Base):

    __tablename__ = 'user_to_perm'

    __table_args__ = (UniqueConstraint('user_id', 'permission_id'), {'extend_existing':True})

    user_to_perm_id = Column("user_to_perm_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)

    permission_id = Column("permission_id", Integer(), ForeignKey('permissions.permission_id'), nullable=False, unique=None, default=None)

    user = relationship('User')

    permission = relationship('Permission')

    @classmethod

    def has_perm(cls, user_id, perm):

        if not isinstance(perm, Permission):

            raise Exception('perm needs to be an instance of Permission class')

        return Session.query(cls).filter(cls.user_id == user_id)\

            .filter(cls.permission == perm).scalar() is not None

    @classmethod

    def grant_perm(cls, user_id, perm):

        if not isinstance(perm, Permission):