def getall(self):
        try:
            spec = {'data': {'$exists': 1}}
            fields = {'_id': 0}
            sort = [('tid', 1)]
            cur = self.db.docs.find(spec, fields, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        return [Document(**row) for row in cur]
def loss_density(isa, subreg=[], ax=0):
    """plot loss density of NC/I7/ISA7 model
    Args:
      isa: Isa7/NC object
    """
    if subreg:
        if isinstance(subreg, list):
            sr = subreg
        else:
            sr = [subreg]
        elements = [e for s in sr for sre in isa.get_subregion(s).elements()
                    for e in sre]
    else:
        elements = [e for e in isa.elements]

    lossd = np.array([e.loss_density*1e-3 for e in elements])
    _contour(ax, 'Loss Density kW/m³', elements, lossd)