Support previously existing Entities

This is definitely a problem, but the approach in this patch is not quite right.
I can see scenarios in which you would NOT want to automatically match existing entities.
Or where we want to match existing entities, but not on the same key we're using for upserts.
Lastly, this won't work for mappings which do not have any key.

This code seems a bit brittle, in that I'm running into situations, where $keyfield is not set, and errors like...

EntityFieldQueryException: Field storage engine not found. in EntityFieldQuery->queryCallback() (line 1190 of                             
/vagrant/public/includes/entity.inc).

...are triggered as a result (I think). I tried wrapping that EFQ in the patch in a check that $keyfield exists. But my understanding of the problem/code at this point makes me feel like a monkey banging on it with a hammer. Also, doing the leads to what seems like several of the same record with only slightly different SalesForce IDs.

I was having the same issue and was able to make it work by implementing hook_salesforce_pull_mapping_object_alter and creating the mapping object if there is a Drupal entity with the same value for the key field.

/**
 * Implements hook_salesforce_pull_mapping_object_alter().
 *
 * @param mixed $mapping_object
 *   The mapping object that was detected based on existing mappings or FALSE
 *   if no exisitng mapping object exists.
 * @param array $sf_object
 *   The salesforce object data that will be used in this pull.
 * @param SalesforceMapping $mapping
 *   The salesforce mapping that will be used during the pull.
 */
function ppu_salesforce_mapping_salesforce_pull_mapping_object_alter(&$mapping_object, $sf_object, $mapping) {
  if (!$mapping_object) {
    // Look for an existing entity by key field and create a mapping object.
    foreach ($mapping->field_mappings as $field_mapping) {
      if ($field_mapping['key'] == TRUE) {
        $keyfield = $field_mapping;
      }
    }
    if (!isset($keyfield)) {
      return FALSE;
    }
    $result = db_select('rsa_places_map', 'p')
      ->fields('p', array('id'))
      ->condition($keyfield['drupal_field']['fieldmap_value'], $sf_object[$keyfield['salesforce_field']['name']], '=')
      ->execute()
      ->fetchAssoc();
    if (!empty($result)) {
      $entity_id = $result['id'];
      // Create mapping object.
      $mapping_object = entity_create('salesforce_mapping_object', array(
        'salesforce_id' => $sf_object['Id'],
        'entity_type' => $mapping->drupal_entity_type,
        'entity_id' => $entity_id,
      ));
      $mapping_object->save();
    }
  }
}

My issue in #4 was that somehow my mapping had been created without a key field actually set. Which shouldn't be possible as it is a required field. I'm not sure how that situation occurred (possibly Features?).

At the very least the affected code has been changed since the patch was last written, so it needs to be rerolled.

FYI I'm not having this problem with the current codebase, but I am seeing it trying to create duplicate 'salesforce_mapping_object' records.

7.x is no longer supported