Question With Relation Widget

Hi, I’m using Relation Widget, for a MANY-TO-MANY relation,

I can see related data, add (show) new combos in the update mode.

But I can’t figure out how to save the related data !

I’m using this to retrive asigned values, but nothing is returned.

            $model->CuotaAnual = Relation::retrieveValues($_POST['Alumno']);

Retrive values doesen’t return nothing.

The HTML generated is a Select input type field.

<select name="Alumno[CuotaDefAnual][1]" id="Alumno_CuotaDefAnual_1">

<option value=""></option>

<option value="1" selected="selected">Cuotas Primaria 1ro EP </option>

<option value="4">Cuotas Primaria 2º y 3º</option>

<option value="5">Cuotas Primaria 1ro a 3ro</option>

<option value="6">Cuotas Primaria 4º, 5º y 6º</option>

<option value="7">Cuotas Secundario 1ª, 2ª y 3ª</option>

<option value="8">Cuotas Secundario 4ª, 5ª y 6ª</option>

<option value="9">Cuotas Nivel Inicial</option>

<option value="10">Cuotas Nivel Inicial</option>

<option value="11">Cuotas Primaria (EP 1ro/2do/3er) </option>

<option value="12">Cuotas Nivel Maternal</option>

<option value="14">Matrícula 2014</option>


Any sugestion how to deal with that in Update Action and also create action.

Best Regards