purchase_order_lider_constructora/views/sale_purchase_discount_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record id="sale_purchase_discount_search_form_view" model="ir.ui.view">
           <field name="name">sale.purchase.discount.search.form</field>
           <field name="model">sale.purchase.discount</field>
           <field name="arch" type="xml">
                <search string="Sale Purchase Discount">
                    <field name="name"/>
                    <field name="type"/>
                </search>
           </field>
        </record>

        <record id="sale_purchase_discount_form_view" model="ir.ui.view">
            <field name="name">sale.purchase.discount.form</field>
            <field name="model">sale.purchase.discount</field>
            <field name="arch" type="xml">
                <form string="Sale Purchase Discount" version="7.0">
                    <sheet>
                        <div class="oe_title">
                            <div class="oe_edit_only">
                                <label for="name" string="Nombre del descuento"/>
                            </div>
                            <h1>
                                <field name="name"/>
                            </h1>
                        </div>
                        <group>
                            <field name="value"/>
                            <field name="type"/>
                        </group>
                    </sheet>
                </form>
            </field>
        </record>

        <record id="sale_purchase_discount_tree_view" model="ir.ui.view">
            <field name="name">sale.purchase.discount.tree</field>
            <field name="model">sale.purchase.discount</field>
            <field name="arch" type="xml">
                <tree string="Sale Purchase Discount">
                    <field name="name"/>
                    <field name="value"/>
                    <field name="type"/>
                </tree>
            </field>
        </record>

        <record model="ir.actions.act_window" id="action_sale_purchase_discount">
            <field name="name">Sale Purchase Discount</field>
            <field name="res_model">sale.purchase.discount</field>
            <field name="view_type">form</field>
            <field name="view_mode">tree,form</field>
        </record>

        <menuitem
            name="Configurar Descuentos"
            id="menu_sale_purchase_discount_parent"
            parent="purchase.menu_purchase_config_purchase"/>

        <menuitem
            name="Descuentos"
            id="menu_purchase_discount"
            action="action_sale_purchase_discount"
            parent="menu_sale_purchase_discount_parent"/>


        <!--
            PURCHASE ORDER
        -->
        <record id="purchase_line_discount_form" model="ir.ui.view">
            <field name="name">purchase.order.form - Confirm</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="//tree[@string='Purchase Order Lines']//field[@name='discount']" position="before">
                    <field name="discount_id" domain="[('type','=','purchase')]"/>
                </xpath>
                <xpath expr="//tree[@string='Purchase Order Lines']//field[@name='discount']" position="attributes">
                    <attribute name="invisible">1</attribute>
                </xpath>
            </field>
        </record>

    </data>
</openerp>