Add optional pass_target_id argument to (#68)

* add optional pass_target_id argument

* style

* Clarify docs; add label when passed entity

src/EntityReferenceConverter.php

@@ -18,13 +18,24 @@ class EntityReferenceConverter {
    *   An array of arguments defined in the mapping.
    *   Expected keys are:
    *     - link_field: The field used to store the URI we will use.
+   *     - pass_target_id: (true/false) should we return a target ID
+   *       when no term is found?
    *
    * @return mixed
-   *   Either the replaced URI string OR the targeted entity if no URI.
+   *   In order of availability:
+   *     - the replaced URI string,
+   *     - the target entity's label,
+   *     - (if pass_target_id is true) the target entity's ID,
+   *     - or an empty string.
    */
   public static function linkFieldPassthrough($target, array $arguments) {
-    if (is_a($target, 'Drupal\Core\Entity\FieldableEntityInterface') && !empty($target->get($arguments['link_field'])->uri)) {
-      return $target->get($arguments['link_field'])->uri;
+    if (is_a($target, 'Drupal\Core\Entity\FieldableEntityInterface')) {
+      if (empty($target->get($arguments['link_field'])->uri)) {
+        return $target->label();
+      }
+      else {
+        return $target->get($arguments['link_field'])->uri;
+      }
     }
 
     if (is_array($target) && array_key_exists('target_id', $target)) {
@@ -35,9 +46,12 @@ public static function linkFieldPassthrough($target, array $arguments) {
       elseif ($ent) {
         return $ent->get('name')->value;
       }
+      elseif (array_key_exists('pass_target_id', $arguments) && $arguments['pass_target_id']) {
+        return $target['target_id'];
+      }
     }
-    // We don't have a value to pass, so don't bother converting.
-    return $target;
+    // Nothing worked, so return nothing.
+    return '';
   }
 
 }