<record model="ir.actions.act_window" id="product_open_bom">
<field name="context">{'default_product_id': active_id, 'search_default_product_id': active_id}</field>
<field name="name">Bill of Materials</field>
<record model="ir.actions.act_window" id="product_open_bom">
<field name="context">{'default_product_id': active_id, 'search_default_product_id': active_id}</field>
<field name="name">Bill of Materials</field>
+ <field name="domain">[('bom_id','=',False)]</field>
<field name="res_model">mrp.bom</field>
</record>
<field name="res_model">mrp.bom</field>
</record>