class CrossUom(DeactivableMixin, ModelSQL, ModelView):
    "Cross Unit of Measure"
    __name__ = 'product.cross_uom'
    name = fields.Function(fields.Char("Name"), 'get_name')
    symbol = fields.Function(fields.Char("Symbol"), 'get_symbol')
    category = fields.Many2One(
        'product.uom.category', "Category", required=True, ondelete='RESTRICT',
        help="The category that contains the unit of measure.\n"
        "Conversions between different units of measure can be done if they "
        "are in the same category.")
    first_uom = fields.Many2One('product.uom', 'First UOM',
        required=True)
    second_uom = fields.Many2One('product.uom', 'Second UOM',
        required=True)
    rate = fields.Float(
        "Rate", digits=uom_conversion_digits, required=True,
        help="The coefficient for the formula:\n"
        "1 (base unit) = coef (this unit)")
    factor = fields.Float(
        "Factor", digits=uom_conversion_digits, required=True,
        help="The coefficient for the formula:\n"
        "coefficient (base unit) = 1 (this unit)")
    rounding = fields.Float(
        "Rounding Precision", digits=(12, Eval('digits', 12)), required=True,
        domain=[
            ('rounding', '>', 0),
            ],
        depends=['digits'],
        help="The accuracy to which values are rounded.")
    digits = fields.Integer(
        "Display Digits", required=True,
        help="The number of digits to display after the decimal separator.")

    def get_name(self, name):
        uom_name = ""
        if self.first_uom and self.second_uom:
            uom_name = "%s by %s" % (self.first_uom.name, self.second_uom.name)
        return uom_name

    def get_symbol(self, name):
        uom_symbol = ""
        if self.first_uom and self.second_uom:
            uom_symbol = "%s/%s" % (self.first_uom.symbol,
                self.second_uom.symbol)
        return uom_symbol