Hello, I want to compute a field based on a number of records in a table.

That I want to do at the finish is :

But with this code, I have an error if I have more than 1 record in the table :

Code :

 class miadi_lignesTarifs(models.Model):
    _name = 'miadi.lignestarifs'
   
    code_tarif = fields.Many2one('miadi.tarifs', 'Price Code', default='', required=True, ondelete='cascade')
    numero_ordre = fields.Integer('Order number', compute='_compute_numero_ordre')
    produit_id = fields.Many2one('product.product', 'Product', required=True, ondelete='cascade')
    conditionnement_id = fields.Many2one('miadi.packaging', 'Packaging', required=True, ondelete='cascade')

    @api.depends('code_tarif')
    def _compute_numero_ordre(self):
        tarifs = self.env['miadi.lignestarifs']
        self.numero_ordre = tarifs.search_count([('code_tarif', '=', self.code_tarif.id)])

Error :

ValueError: Expected singleton: miadi.lignestarifs(17, 18)

I tried to do it overriding the create method :

@api.multi
@api.model
def create(self, vals):
    tarifs = self.env['miadi.lignestarifs']
    self.numero_ordre = tarifs.search_count([('code_tarif', '=', self.code_tarif.id)])
    return super(miadi_lignesTarifs, self).create(vals)

But it gives me this :

TypeError: create() takes exactly 2 arguments (1 given)

How can I do what I want ?

I'm on Odoo 10

Thanks for answers