Hide "Confirm Sale" button in Sale Order form view in Odoo 9

I'm using Odoo 9 community version.

In Sale order form has following buttons:

<button name="action_confirm" states="sent" string="Confirm Sale" class="btn-primary" type="object" context="{'show_sale': True}"/>
<button name="action_confirm" states="draft" string="Confirm Sale" type="object" context="{'show_sale': True}"/>

I'm trying to hide both button from the view. So I have tried with following code.

<record model="ir.ui.view" id="hide_so_confirm_button_form">
    <field name="name">hide.so.confirm.button.form</field>
    <field name="model">sale.order</field>
    <field name="inherit_id" ref="sale.view_order_form"/>
    <field name="arch" type="xml">
        <button name="action_confirm" position="attributes">
            <attribute name="invisible">1</attribute>
        </button>
    </field>
</record>

I have also tried following attribute:

<attribute name="states"></attribute>

With above code, it's only hide/affect first button.

Question:

How to hide both Confirm Sale button?

Solution

The mechanism without xpath only influences the first hit. That's why you have to use xpath here.

Another good example (maybe not for Odoo 9 anymore) is setting a new sale.order.line field behind the name field on sale.order form view. The form view is something like this:

<form>
    <field name="name" /> <!-- sale.order name field -->
    <!-- other fields -->
    <field name="order_line">
        <form> <!-- embedded sale.order.line form view -->
            <field name="name" />
            <!-- other fields -->
        </form>
        <tree> <!-- embedded sale.order.line tree view -->
            <field name="name" />
            <!-- other fields -->
        </tree>
    </field>
<form>

Using your way could try setting the new field behind sale.order name field (in this example). Using xpath will lead to the goal.

<xpath expr="//form//tree//field[@name='name']" position="after">
    <field name="new_field" />
</xpath>
<xpath expr="//form//form//field[@name='name']" position="after">
    <field name="new_field" />
</xpath>

So to answer your question directly (EDIT):

<xpath expr="//button[@name='action_confirm' and @states='sent']" position="attributes">
    <attribute name="states" /> <!-- delete states attribute, it's influencing invisible behaviour -->
    <attribute name="invisible">1</attribute>
</xpath
<xpath expr="//button[@name='action_confirm' and @states='draft']" position="attributes">
    <attribute name="states" /> <!-- delete states attribute, it's influencing invisible behaviour -->
    <attribute name="invisible">1</attribute>
</xpath