[IMP] packaging_uom: declare 'inverse' method on qty

This change is required to make the code working with existing addons without breaking tets. By declaring an invers on qty, we are able to assign/create the required uom to the package based on the expected qty

packaging_uom/models/product_packaging.py

@@ -1,7 +1,8 @@
 # -*- coding: utf-8 -*-
 # Copyright 2015-2017 ACSONE SA/NV (<http://acsone.eu>)
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
-from odoo import api, fields, models
+from odoo import api, fields, models, _
+from odoo.exceptions import ValidationError
 
 
 class ProductPackaging(models.Model):
@@ -18,9 +19,9 @@ class ProductPackaging(models.Model):
     uom_id = fields.Many2one(
         'product.uom',
         'Unit of Measure',
-        required=True,
         help="It must be in the same category than "
-             "the default unit of measure."
+             "the default unit of measure.",
+        required=False
     )
     uom_categ_domain_id = fields.Many2one(
         default=_default_uom_categ_domain_id,
@@ -28,6 +29,7 @@ class ProductPackaging(models.Model):
     )
     qty = fields.Float(
         compute="_compute_qty",
+        inverse="_inverse_qty",
         store=True,
         readonly=True
     )
@@ -43,3 +45,38 @@ class ProductPackaging(models.Model):
                 1, to_unit=self.product_tmpl_id.uom_id)
         else:
             self.qty = 0
+
+    @api.one
+    def _inverse_qty(self):
+        """
+        The inverse method is defined to make the code compatible with
+        existing modules and to not break tests...
+        :return:
+        """
+        category_id = self.product_tmpl_id.uom_id.category_id
+        uom_id = self.uom_id.search([
+            ("factor", "=", 1.0 / self.qty),
+            ('category_id', '=', category_id.id)])
+        if not uom_id:
+            uom_id = self.uom_id    .create({
+                'name': "%s %s" % (category_id.name, self.qty),
+                'category_id': category_id.id,
+                'rounding': self.product_tmpl_id.uom_id.rounding,
+                'uom_type': 'bigger',
+                'factor_inv': self.qty,
+                'active': True
+            })
+        self.uom_id = uom_id
+
+    @api.multi
+    @api.constrains
+    def _check_uom_id(self):
+        """ Check uom_id is not null
+
+        Since the field can be computed by the inverse method on 'qty',
+        it's no more possible to add a sql constrains on the column uom_id.
+        """
+        for rec in self:
+            if not rec.uom_id:
+                raise ValidationError(_("The field Unit of Measure is "
+                                        "required"))

packaging_uom/views/product_packaging_views.xml

@@ -25,7 +25,7 @@
         <field name="arch" type="xml">
             <field name="qty" position="before">
                 <field name="uom_categ_domain_id" invisible="1"/>
-                <field name="uom_id" domain="[('category_id', '=', uom_categ_domain_id)]"/>
+                <field name="uom_id" domain="[('category_id', '=', uom_categ_domain_id)]" required="True"/>
             </field>
         </field>
     </record>