I have three table :

- product.

- package.

- product_package.

The product_package table have 2 fields which are related to the product and package as it mentionned bellow :

product_id = fields.Many2one('tjara.product', ondelete='cascade', string="Produit", index=True)
package_id = fields.Many2one('tjara.package', ondelete='cascade', string="Emballage", index=True)
_sql_constraints = [
        ('ligne_unique', 'unique (product_id, package_id)', '%(package_id)d Package is already exists for this product...!')
    ]

I added the _sql_contraints to avoid the duplicate fields. Because it can be only an unique relation between the product and a package.

And this is what I have in the product model :

product_package_ids = fields.One2many('tjara.product_package', 'product_id', string='Package')

And this is how to add a package from the product view :

                                <page string="Package">
                                    <label for="product_package_ids" string="Emballage"/>
                                    <field name="product_package_ids">
                                        <tree>
                                            <field name="package_id"/>
                                            <field name="price"/>
                                        </tree>
                                        <form>
                                             <field name="package_id"/>
                                            <field name="price"/>
                                        </form>
                                    </field>
                                </page>

This works fine for me. There is only one thing I want to enhance. When the user select an existing package for the product there is no error triggered. The error popped up only when you click "save the product".

I want either to display only the unexisting packages in the select field package_id. Or to pop up an error when the user try to add an existing package for the product.