i want to add to add new field "arabic_name" to  signup page i add the field in res.partner
,add it to the sign up view , and override the def_prepare_signup_values  and add my new field 
but the field in the sign up deoen't stored or related to the field on res.partner 
what i do 
1-override  _prepare_signup_values function
class ExtendAuthSignupHome(AuthSignupHome):
    	def _prepare_signup_values(self, qcontext):
        		values = { key: qcontext.get(key) for key in ('login', 'name', 'password' , 'arabic_name') }
        	if not values:
            		raise UserError(_("The form was not properly filled in."))
        	if values.get('password') != qcontext.get('confirm_password'):
            		raise UserError(_("Passwords do not match; please retype them."))
        	supported_lang_codes = [code for code, _ in request.env['res.lang'].get_installed()]
        	lang = request.context.get('lang', '')
        	if lang in supported_lang_codes:
            	values['lang'] = lang
        	return values
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2-add field to res.partner
class MoreField(models.Model):
    	_inherit = 'res.partner'
    	arabic_name = fields.Char(string="Name In Arabic")
=====================
3-add field to the signup view
expr="//div[@class='form-group field-name']" position="after">
	
	
	type="text" name="arabic_name" t-att-value="arabic_name" id="arabic_name" 	class="form-control form-control-sm" placeholder="e.g. أحمد على"
	required="required" t-att-readonly="'readonly' if only_passwords else None"
	t-att-autofocus="'autofocus' if login and not only_passwords else None" />
	
