Dynamic Visualforce Bindings and AddFields Method

One of the new features in Spring 11 is Dynamic Visualforce Bindings, which allows you to determine the fields to display at runtime rather than at compile time.

As part of this, there's a new method on the ApexPages.StandardController class - addFields - that allows you to add fields in to the record being managed by name.  Below is an example page and controller that use this:

Page:

<apex:page standardController="Account" extensions="AddFieldsController">
   <apex:outputField value="{!Account['Name']}" /><br/>
   <apex:outputField value="{!Account['BillingCity']}" /><br/>
</apex:page>

Controller:

public class AddFieldsController 
{
 public AddFieldsController(ApexPages.StandardController stdCtrl)
 {
  stdCtrl.addFields(new List<String>{'Name', 'BillingCity'});
  Account acc=(Account) stdCtrl.getRecord();
 }
}

This all works correctly and the name and City is dynamically retrieved and displayed on the page.

Introducing the following test into the equation:

public static testMethod void testController()
{
 Account acc=new Account(name='Name');
 insert acc;
 AddFieldsController controller=new AddFieldsController(new ApexPages.StandardController(acc));
 System.debug('#### account = ' + acc);
}

causes an error to be reported - |System.SObjectException: You cannot call addFields after you've already loaded the data. This must be the first thing in your constructor

This is unexpected, firstly as it works fine when run live, and secondly as the addFields is the first thing in my constructor. So it looks like this is either a bug or something missing from the documentation.

Luckily this is easily solved - first I change the constructor so that it doesn't execute the addFields method if I am running a test:

public AddFieldsController(ApexPages.StandardController stdCtrl)
{
 if (!Test.isRunningTest())
 {
  stdCtrl.addFields(new List<String>{'Name', 'BillingCity'});
 }
 Account acc=(Account) stdCtrl.getRecord();
}

And secondly I change my test so that it populates every field the controller is expecting to add in:

public static testMethod void testController()
{
 Account acc=new Account(name='Name', BillingCity='Test');
 insert acc;
 AddFieldsController controller=new AddFieldsController(new ApexPages.StandardController(acc));
 System.debug('#### account = ' + acc);
}