Symfony Set基于ID的下拉值

I am still getting my hands dirty with Symfony, so I am a bit ignorant on how to do something that should be pretty simple.

I have a form that I am creating in the controller and passing to the view:

 $form = $this->createForm(new PurchaseOrderType($account), $purchaseOrder);

The form displays exactly how I need it to, no problems at all! I am trying to now make the form more dynamic so that it can auto select a drop down list based upon an "id" variable that I am passing into the form. The id equals 23 by the way.

So, I have a drop down of suppliers and one of the options value is 23. How do I automatically select this option? Sorry for my ignorance :)

Thanks!

Without the code of your form type, I can make only suggestion.

If I get it correctly, inside the purchase order entity, there is an other entity mapped, and that one is represented with an id. The object, $purchaseOrder has to have the other entity, then in the form type, when you set up the drop down field, you have to specify - with the correct name it shouldn't be a problem - the foreign id. But you need of course data for the drop down field what can be the result of a SELECT * query.