odoo-membership-addons/membership_initial_discount/models/product_product.py

# License AGPL-3 - See https://www.gnu.org/licenses/agpl-3.0
from odoo import models, fields, api, _
from odoo.exceptions import ValidationError


class ProductProduct(models.Model):
    _inherit = "product.product"

    @api.constrains("lst_price", "initial_discount", "fixed_discount")
    def check_discount_fixed(self):
        for product in self:
            if (
                product.initial_discount == "fixed"
                and product.lst_price <= product.initial_discount
            ):
                raise ValidationError(
                    _(
                        "Fixed discount for 1st membership must be less than the product template or any of its variants sale price."
                    )
                )