How do I find out if a field is updateable by the System?

Question

I am running a batch process that is marked without sharing.

I would like to to take one course of action if the batch process can update a particular field, and another if not.

For example:

if (canUpdate(fld)) {
  updateRecord();
} else {
  cloneRecordAndUpdateThat();
}

The naive way of writing canUpdate() is to use fld.getDescribe().isUpdateable(). However, that will always look at the current user's permissions. I specifically want to override user permissions, but sometimes fld is not updateable on a system level (e.g., the "master" field on a master-detail relationship that cannot be reparented).

How do I discover if "god-mode" without sharing permissions can update that field?

Answer 1

I had this partway there, and you're welcome to check out and adapt my code that hits the Tooling API to discover if a Detail side of MasterDetail can be reparented, and makes a number of other assumptions about fields.

I then realized how complex it would be to maintain RemoteSiteSettings for developer and training sandboxes. But the straw that broke my code's back was discovering that batch processes and @future methods don't have UserInfo.getSessionId(), so I'd need an OAuth refresh_token.... All told, that was too much for me to deal with, so I went the route suggested in the comment above by Jigar.

It turns out, the exception thrown is not a DmlException, but an SObjectException with the message "Case__c is not editable", and it happens when you set the field, well before the update.

Below is my solution:

Boolean shouldCreateClones = false;
try {
  updateRecords(scope);  
} catch (System.SObjectException ex) {
  if (ex.getMessage().contains('is not editable')) {
    shouldCreateClones = true;
  } else {
    throw ex;
  }
}

if (shouldCreateClones) {
  cloneRecordsAndUpdateThose(scope);
}