Hi Miadi,

To add a field to the product.product model first you have to inherit that model and has to define that model, like this

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

    test_field = fields.One2many('test.model', 'connect_test_model', string='Packaging')
    

class TestModel(models.Model):
    _name = 'test.template'

    connect_test_model = fields.Many2one('product.template', string="Connect")
    customer_id = fields.Char(string="Passenger")
    age = fields.Integer(string="Age")

Then in the XML,

<record model="ir.ui.view" id="view_variantes_conditionnement_form">
    <field name="model">product.template</field>
    <field name="name">view.inherit.variantes.conditionnement.form</field>
    <field name="inherit_id" ref="product.product_template_form_view"/>
    <field name="arch" type="xml">
             <xpath expr="//page[@name='notes']" position="after">
                   <page name="miadi_variantes_conditionnement" string="Packaging">
                           <field name="test_field" >
                                <tree editable="bottom">
                                    <field name="customer_id"/>
                                    <field name="age"/>
                                </tree>
                            </field>
                   </page>
             </xpath>
    </field>
</record>

Thank You

Codes :

class miadi_packaging(models.Model):
	_name = 'miadi.packaging'
	_rec_name = 'conditionnement_id'
	_order = 'conditionnement_id asc'
	conditionnement_id = fields.Char(string='Code', size=4, default='', required=True)
	conditionnement_nom = fields.Char(string='Packaging Name', default='', required=True)
	nb_articles = fields.Integer(string='Number of products', default=0, required=True)
	poids = fields.Float(string='Weight', default=0, required=True)
	type = fields.Many2one('miadi.packaging.type', 'Type of Packaging', default='', required=True)
	_sql_constraints = [
	('uniq_id', 'unique(conditionnement_id)', 'A packaging already exists with this ID. It must be unique !'),
	('uniq_name', 'unique(conditionnement_nom)', 'A packaging already exists with this name. It must be unique !'),
	]

class miadi_poidsConditionnement(models.Model):
	_name = 'miadi.poidsconditionnement'
	conditionnement_id = fields.Many2one('miadi.packaging', 'Packaging', default='', required=True)
	produit_id = fields.Many2one('product.product', 'Product', default='', required=True, ondelete='cascade')
	nb_articles = fields.Integer(string='Number of products', default=0)
	poids = fields.Float(string='Packaging Weight', default=0)
	
	_sql_constraints = [
	('uniq_id', 'unique(produit_id, conditionnement_id)', 'A product already exists with this packaging !'),
	]
	
	@api.multi
	@api.model
	def chargement_ratio(self):
		productRatio = self.env['miadi.poidsconditionnement']
		conditionnements = self._cr.execute("SELECT id FROM miadi_packaging")
		query_cond = self.env.cr.dictfetchall()
		produits = self._cr.execute("SELECT id FROM product_product")
		query_prod = self.env.cr.dictfetchall()
		for conditionnements in query_cond:
			nom_conditionnement = conditionnements['id']
			for produits in query_prod:
				product = produits['id']
				if_exist = self._cr.execute("SELECT * FROM miadi_poidsConditionnement WHERE conditionnement_id=%s AND produit_id=%s", (nom_conditionnement, product))
				exist = self.env.cr.dictfetchall()
				if exist:
					if_actif = self._cr.execute("SELECT active FROM product_product WHERE id=%s", (product,))
					state_actif = self.env.cr.dictfetchone()
					actif = state_actif['active']
					if actif == False:
						productRatio.search([('produit_id', '=', product), ('conditionnement_id', '=', nom_conditionnement)]).unlink()
				if not exist:
					if_actif = self._cr.execute("SELECT active FROM product_product WHERE id=%s", (product,))
					state_actif = self.env.cr.dictfetchone()
					actif = state_actif['active']
					if actif == True:
						Ratio = productRatio.create({'conditionnement_id': nom_conditionnement, 'produit_id': product})
		return {'name': _('Weight/number Ratio'), 'view_type': 'form', 'view_mode': 'tree', 'view_id': self.env.ref('miadi_packaging.miadi_poidsConditionnement_tree').id, 'res_model': 'miadi.poidsconditionnement', 'type': 'ir.actions.act_window', 'target': 'current',}
	
class ProductProduct(models.Model):
    _inherit = 'product.template'
    packaging_quantity = fields.Char(string="kkkkk")

<?xml version="1.0" encoding="utf-8"?>
<openerp>
	<data>
		<record id="miadi_poidsConditionnement_form" model="ir.ui.view">
			<field name="name">miadi.poidsconditionnement.form</field>
			<field name="model">miadi.poidsconditionnement</field>
			<field name="arch" type="xml">
				<form string="Weight/number ratio">  
					<group col="4">
						<field name="produit_id" />
						<field name="conditionnement_id" />
						<field name="nb_articles" />
						<field name="poids" />
					</group>
				</form>
			</field>
		</record>
		
		<record id="miadi_poidsConditionnement_tree" model="ir.ui.view">
			<field name="name">miadi.poidsconditionnement.tree</field>
			<field name="model">miadi.poidsconditionnement</field>
			<field name="arch" type="xml">
				<tree string="Weight/number ratio" editable="top">
					<field name="produit_id" ref="product.product.attribute_value_ids" />
					<field name="conditionnement_id" ref="miadi.packaging.conditionnement_id" />
					<field name="nb_articles" />
					<field name="poids" />
				</tree>
			</field>
		</record>
		
		<record model="ir.ui.view" id="miadi_poidsConditionnement_search">
			<field name="name">miadi.poidsconditionnement.search</field>
			<field name="model">miadi.poidsconditionnement</field>
			<field name="arch" type="xml">
				<search string="Weight/number ratio">
					<field name="produit_id" />
					<group expand="0" string="Group by">
						<filter string="Product" domain="[]" context="{'group_by':'produit_id'}"/>
						<filter string="Packaging" domain="[]" context="{'group_by':'conditionnement_id'}"/>
					</group>
				</search>
			</field>
		</record>
		
		<record model="ir.actions.act_window" id="action_miadi_poidsConditionnement">
			<field name="name">Weight/number ratio</field>
			<field name="type">ir.actions.act_window</field>
			<field name="res_model">miadi.poidsconditionnement</field>
			<field name="view_type">form</field>
			<field name="view_mode">tree,form</field>
			<field name="view_id" ref="miadi_poidsConditionnement_tree"/>
			<field name="help" type="html">
				<p class="oe_view_nocontent_create">Click here to create a weight/number ratio.</p>
			</field>
		</record>
		
		<record id="action_chargement_ratio" model="ir.actions.server">
			<field name="name">Chargement Ratio</field>
			<field name="type">ir.actions.server</field>
			<field name="model_id" ref="model_miadi_poidsconditionnement"/>
			<field name="code">action = env['miadi.poidsconditionnement'].chargement_ratio()</field>
		</record>
		
		<menuitem name="Weight/number ratio" id="menu_miadi_poidsConditionnement" parent="menu_miadi_packaging" sequence="15" action="action_chargement_ratio" />
		
		 
		
	</data>
</openerp>

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record model="ir.ui.view" id="view_variantes_conditionnement_form">
            <field name="model">product.template</field>
            <field name="name">view.inherit.variantes.conditionnement.form</field>
            <field name="inherit_id" ref="product.product_template_form_view"/>
            <field name="arch" type="xml">
                <xpath expr="//page[@name='notes']" position="after">
                    <page name="miadi_variantes_conditionnement" string="Packaging">
                        <tree string="Packaging" editable="bottom">
                            <field name="packaging_quantity" />
                        </tree>
                    </page>
                </xpath>
            </field>
        </record>
    </data>
</openerp>

I've a table (miadi.poidsconditionnement) which gives a treeview with some records taking products (from product.product) and packaging (from miadi.packaging).

When I go to the form view of a product variant, I want to display in the created page, all records from the miadi.poidsconditionnement table for the product where I am. (Or, if it's possible, I want to execute a function with SQL queries and this function returns a treeview that will be display in the created page)

Do you understand ? If yes, can you help me to edit my code ?

Thank you