Can't get Custom Object ParentID for Attachment save

Question

I'm uploading an attachment via "sforce" following the example here:

Upload attachment in VisualForce without reloading the whole page

However I'm having problems getting a value for ParentId. I first tried to instantiate a new custom object in my controller constructor like this:

public Custom_object__c attachmentParent {get; set;}

public MyControllerConstructor() {
        attachmentParent = new Custom_object__c(Name="temp");
        insert attachmentParent;
    }

But when I'm in the visualforce page and I try to set the parentId field to {!attachmentParent.Id} it comes back blank. How am I supposed to do this?

Answer 1

You cannot perform any DML in the constructor. If you really want to create a new parent on the fly for this page, use the action attribute on your page tag.

<apex:page controller="MyController" action="{!createParent}">

Then in your controller:

public PageReference createParent()
{
    attachmentParent = new Custom_object__c(Name="temp");
    insert attachmentParent;
    return null;
}