cooperative-market/partner_firstname/models/partner.py

from odoo import models, fields, api, _
from odoo.exceptions import ValidationError

def concat_names(*args):
    """
        Concatenate only args that are not empty
        @param args: a list of string
    """
    return ' '.join(filter(bool, args))

class Partner(models.Model):

    _inherit = 'res.partner'

    firstname = fields.Char('First Name')
    lastname = fields.Char('Last Name', required=True, default="/")
    name = fields.Char(compute='_get_name', inverse='_set_name', store=True, string="Full Name")

    @api.depends('firstname', 'lastname')
    def _get_name(self):
        for rec in self:
            rec.name = concat_names(rec.firstname, rec.lastname)

    def _set_name(self):
        """
            This allow to handle the case of code that write directly on the name at creation
            Should never happen but in case it happen write on the lastname
            If there is no firstname lastname and name are the same
        """
        for rec in self:
            if not rec.firstname:
                rec.lastname = rec.name

    #Compatibility with old name use in beedoo
    last_name = fields.Char(related='lastname', string="Last Name (Legacy)")
    first_name = fields.Char(related='firstname', string="Frist Name (Legacy)")