Hi Cyril Gaspard,

Thanks to you for answer. 

Now, I have this:

prepare_adv()
 _______________________________________________________________________
|      Ref:  ______________                             Period: _________ - ___________       |
|      _button_here                                                                                                   |
|............................................................................................................................|
|      ________________________________________________________________      |
|      |    id     |     employee      |   wage_of_contract   |   compute_40%_of_wage   | <---|----  this is my adv()
|      |-----------|-------------------------|--------------------------------|----------------------------------------|       |

adv.id and adv.employee have in hr_employee, and adv.wage_of_contract have in hr_contract, now, adv.compute_40%_of_wage is automatic compute from adv.wage_of_contract.
I need create this every month but one time, with all employee available. I solved the problem to save datas in adv() and can see this in prepare_adv() but have other problem :)
The problem is the next: when is only one row fine, save and can see perfect; but if it is more than one row show the next error: 

Expected singleton: hr.py.advances(104, 105, 103)

Save the data in adv() but show the error mentioned.
I have understood that need create new rows for news records. 

This is my code of function from button (this are in prepare_adv()): 

def on_click(self, cr, uid, ids, context=None):
        res = {}
        for adv in self.browse(cr,uid,ids):
            cr.execute('''SELECT hr_employee.id, id_inter, wage FROM hr_employee, hr_contract WHERE hr_employee.id=employee_id''')
            temp = cr.fetchall()
            per = time.strftime('%m/%Y')
            for record in temp:
                datas = {'advances_id':adv.id,'period_id':per,'id_intern':record[1],'employee_name':record[0],'wage_base':record[2]}
                crea = self.pool.get('hr.py.advances').create(cr,uid,datas,context=context)
                self.pool.get('hr.py.advances').write(cr,uid,crea,datas,context=context)
            return True

This is my adv() class:

class adv(models.Model):
    _name = 'adv'

    advances_id = fields.Many2one('prepare.adv')
    period_id = fields.Char()
    id_intern = fields.Integer(string='Cod.')
    employee_name = fields.Many2one('hr.employee', string='Funcionario')
    wage_base = fields.Float(string='Salario')
    advances_40 = fields.Integer(compute='_compute_wage_advance', string='40% Adelanto Quinc.')

    @api.depends('wage_base')
    def _compute_wage_advance(self):
        self.advances_40 = self.wage_base * 0.40

This id my prepare_adv() class:

class prepare_adv(models.Model):
    _name = 'prepare.adv'

    state = fields.Selection([('draft','Borrador'),('done','Aprobado')], default='draft', string='Status', select=True, readonly=True, copy=False)
    referenc = fields.Char(string='Referencia',default='Anticipo - ' + time.strftime('%m/%Y'))    
    date_from = fields.Datetime(string='Periodo', default=lambda *a: time.strftime('%Y-%m-01'), required=True, readonly=True, states={'draft': [('readonly', False)]})
    date_to = fields.Datetime(string='-', default=lambda *a: str(datetime.now() + relativedelta.relativedelta(months=+1, day=1, days=-1))[:10], required=True, readonly=True, states={'draft': [('readonly', False)]})
    per_id = fields.Char(string='per', default= time.strftime('%m/%Y'))
    advancs = fields.One2many('adv','advances_id')

This is the view of prepare_adv():

<div class="oe_title">
                            <label for="referenc" class="oe_edit_only"/>
                            <h1>
                                <field name="referenc"/>
                            </h1>
                        </div>
                        <div class="oe_right">
                            <label for="date_from" class="oe_edit_only"/><field name="date_from" class="oe_inline"/><label for="date_to">-</label><field name="date_to" class="oe_inline"/>
                        </div>
                        <group>
                            <button string="Cargar" name="charge_employee" states="draft" type="object" class="oe_highlight"/>
                        </group>
                        <notebook>
                            <page>
                                <field name="advancs" nolabel="1"/>
                            </page>
                        </notebook>

How create news row for view all amount of employee (around of 72 employee)?