Can I avoid creating a new revision of every attached field upon entity save?

Question

I have created a custom entity with several properties and several attached fields.

When I load a instance of my custom entity, update a property of the entity (e.g UID) and save it a new revision of the entity is created, but also a new revision of every attached field is created.

To avoid saving lots of redundant data I only really want to create a new revision of an attached field if the data in that field has changed.

I've noticed that this same behavior is exhibited by core node objects, but is still not really desirable.

My function which currently saves my entity looks like this:

/**
* Saves a emtr safe check to the database.
*
* @param $emtr_safe_check
*   The emtr_safe_check object.
*/
function emtr_safe_check_save(EMTRSafeCheck $emtr_safe_check) {

    $is_new = isset($emtr_safe_check->is_new) ? $emtr_safe_check->is_new : false;

    // always make a new revision
    $emtr_safe_check->is_new_revision = TRUE;
    $emtr_safe_check->save();

    if($is_new) {
        // now we have the new emtr safe check id lets save the attached fields
        field_attach_insert('emtr_safe_check', $emtr_safe_check);
    } else {
        // This is where my attached fields are saved
        // Can I do something clever here to avoid creating redundant revisions?
        field_attach_update('emtr_safe_check', $emtr_safe_check);
    }

    return $emtr_safe_check;
}

Answer 1

I have looked around and found one HACKY solution. I think it probably has some serious side effects that you may be able to handle with custom code and db queries. This is definitely not a generic solution.
I did my test on the node entity and every thing worked fine in my 5 min test case. Here is what I did:

function playground_node_presave($node){
  dpm($node);
  // do a query here and check if the value is in the field_revision_table is
  // equal to the value on the node/entity object.
  unset($node->field_cookies);
  dpm($node);
  // The node will be saved without changing the value of the field and without creating 
  // creating a new entry in the field_revision_table.
}