RFC: product_template_multi_link improvement.

[lmignon]

In the current implementation, when you add a link from product a to product b, the reverse link is not shown on product b (even if the information exists). Moreover it's not possible to define new types of link without extending the addon.

I propose to improve the implementation to fix these to issues. It could look like

class ProductLinkType(models.Model):
    _name='product.link.type"

    name = fields.Char()
    inverse_name = fields.Char()


class ProductLink(models.Model):
    _name='product.link"

   product_tmpl_id_left = fiedls.Many2one()
   product_tmpl_id_right = fiedls.Many2one()  
   product_link_type = fields.Many2one()
   link_type_name = fields.Char(related="product_link_type.name") # left to right
   link_type_inverse_name = fields.Char(related="product_link_type.invese_name") # right to left

    @api.multi
    @api.constrains("product_tmpl_id_left", "product_tmpl_id_right")
    def _check_products(self):
        """
        This method checks whether:
            - the two products are different
            - there is only link between the same two templates for the same type
        :raise: ValidationError if not ok
        """
       pass

class ProductTemplate(models.Model):
    _inherit = "product.template"

    product_link_ids = fields.One2many(comodel_name="product.link")
        compute="_compute_product_link_ids",
    )


    @api.multi
    def _compute_product_link_ids(self):
        link_model = self.env["product.link"]
        domain = [
            "|",
            ("product_tmpl_id_left", "in", self.ids),
            ("product_tmpl_id_right", "in", self.ids),
        ]
        links = link_model.search(domain)
        links_by_product_id = defaultdict(link_model.browse)
        for link in links:
            links_by_product_id[link.product_tmpl_id_left.id] |= link
            links_by_product_id[link.product_tmpl_id_right.id] |= link
        for record in self:
            record.product_link_ids = links_by_product_id[
                record.id
            ]

With this kind of implementation:

• it become easy to export the links between products with the right semantic depending of the place of the product into the relation (left of right)
• when product a is linked to b, b is linked to a
• it's easy to display all the links for one product
• you are not restricted to the predefined list of link types
• ????