Hi,

there is one button to confirm draft purchase order is like below.

<button name="purchase_confirm" states="draft" string="Confirm Order" id="draft_confirm"/>

here this button is of type "workflow". Because if type is not specify then default it is workflow type.

So, we need to see the "purchase_confirm" signal into the purchase workflow. There are many transition in that you can find out the signal with name "purchase_confirm". It is as like below.

<record id="trans_draft_confirmed" model="workflow.transition">

<field name="act_from" ref="act_draft"/>

<field name="act_to" ref="act_confirmed"/>

<field name="signal">purchase_confirm</field>

</record>

When workflow signal is fire then workflow activity is transfer act_from to act_to. Here "act_draft" is from and "act_confirmed" is to activity. So, workflow activity is moving from "act_draft" to "act_confirmed".

So, when you click on the button string="Confirm Order" at that time method of the act_to (here it is "act_confirmed") is called. Activity is like below.

<record id="act_confirmed" model="workflow.activity">

<field name="wkf_id" ref="purchase_order"/>

<field name="name">confirmed</field>

<field name="split_mode">OR</field>

<field name="kind">function</field>

<field name="action">wkf_confirm_order()</field>

</record>

So, based on this flow you need to update / edit one method with named "wkf_confirm_order".

You will get your desire result.