openerp.purchase_requisition = function(instance) {
    var QWeb = instance.web.qweb,
        _t = instance.web._t;

    instance.web.purchase_requisition = instance.web.purchase_requisition || {};

    instance.web.views.add('tree_purchase_order_line_compare', 'instance.web.purchase_requisition.CompareListView');
    instance.web.purchase_requisition.CompareListView = instance.web.ListView.extend({
        init: function() {
            var self = this;
            this._super.apply(this, arguments);
            this.on('list_view_loaded', this, function() {
                if(self.__parentedParent.$el.find('.oe_generate_po').length == 0){
                    var button = $("<button type='button' class='oe_button oe_highlight oe_generate_po'>Generate PO</button>")
                        .click(this.proxy('generate_purchase_order'));
                    self.__parentedParent.$el.find('.oe_list_buttons').append(button);
                }
            });
        },
        generate_purchase_order: function () {
            var self = this;
            new instance.web.Model(self.dataset.model).call("generate_po",[self.dataset.context.active_id,self.dataset.context]).then(function(result) {
                self.ViewManager.ActionManager.history_back();
            });
        },
    });
}