I'm very new on ODOO. I'm trying to validate the purchase orders VS a custom field (quantity permited by certain supplier).

I've created a module with the following:

models.py

from odoo import models, fields, api

class SupplierInfoInherited(models.Model):
    _inherit = 'product.supplierinfo'

quantity = fields.Integer(string='Quantity allowed for this supplier')

On view.xml:

<odoo>
<!--Inherit the supplier form view--> 
<record id="view_supplier_form_custom" model="ir.ui.view"> 
<field name="name">product.supplierinfo.form.inherited</field>
    <field name="model">product.supplierinfo</field> 
    <field name="inherit_id" ref="product.product_supplierinfo_form_view"/> 
    <field name="arch" type="xml"> 
        <xpath expr="//field[@name='product_id']" position="after"> 
            <field name="quantity"/>
        </xpath> 
    </field> 
</record>

Now i'm need get this value on purchases.order.line and validate that the quantity of products does not exceed the amount determined in the custom rule, using javascript/python at the moment of purchase. Any ideas? thanks