How to programmatically get the difference between two entities of same content type?
Either look at:


https://www.drupal.org/project/diff
https://www.drupal.org/project/html_diff


To easily "see" if changes exist. Or look at Migrates module track_changes implementation and implement it in code between revisions. All track_changes does is hash the fields of a content type together to get a unique ID. Different revisions of a node with changes between the body field will of course hash to a different value. Be sure to exclude node fields such as NID, vid, updated_at and other fields that (may) chnage between revisions.

Sample hash code from class MigrateSource:

// When tracking changed data, We want to quietly skip (rather than
// "ignore") rows with changes. The caller needs to make that decision,
// so we need to provide them with the necessary information (before and
// after hashes).
if ($this-&gt;trackChanges) {
    $unhashed_row = clone ($row);
    // Remove all map data, otherwise we'll have a false positive on the
    // second import (attempt) on a row.
    foreach ($unhashed_row as $field =&gt; $data) {
      if (strpos($field, 'migrate_map_') === 0) {
        unset($unhashed_row-&gt;$field);
      }
    }
    $row-&gt;migrate_map_original_hash = isset($row-&gt;migrate_map_hash) ?
      $row-&gt;migrate_map_hash : '';
    $row-&gt;migrate_map_hash = $this-&gt;hash($unhashed_row);
  }
  else {
    $row-&gt;migrate_map_hash = '';
  }