i want to hide the field "parent_id"  in the 'hr.department' form view if the field "scale" equal to "top" 

the thing is the "scale" field from diffrent class than the partner_id 

in my model.py 

class depart_typ(models.Model):

    _inherit = "hr.department"

    depart_typ = fields.Many2one('department.type', 'Type')

class depart_line(models.Model):

    _name = "department.type"

    _description = "Type Hierarchie"

    nom_typ = fields.Char(string="Nom")

    scale =  fields.Selection([ ('type1', 'top'),('type2', 'intermed'),('type3', 'child'),],'Niveau', default='type2')

and on my xm file 

<record id="view_hr_department_inherit" model="ir.ui.view">

                <field name="name">hr.department.form.inherit</field>

                <field name="model">hr.department</field>

                <field name="inherit_id" ref="hr.view_department_form"/>

                <field name="arch" type="xml">

                    <xpath expr="//form/sheet/group/field[@name='parent_id']" position="before">

                        <field name="depart_typ">

                            <form>

                                <group>

                                    <field name="scale"/>

                                    <field name="parent_id" string="Unité fonctionnement Parent" attrs="{'invisible':[('scale', '==', 'type1')]}"/>

                                    <field name="nom_typ"/>

                                </group>

                            </form>

                        </field>

                    </xpath>

                </field>

    </record>

and i get the error that the partner_id dosen't exist 

which is totally logical, the filed in not on the same classe. is there any solution ?