Issue #3285438: Prevent index clear when field mapping hasn't changed.

src/SearchAPI/BackendClient.php

@@ -269,7 +269,6 @@ class BackendClient implements BackendClientInterface {
    */
   public function updateIndex(IndexInterface $index): void {
     if ($this->indexExists($index)) {
-      $index->clear();
       $this->updateSettings($index);
       $this->updateFieldMapping($index);
     }
@@ -291,6 +290,9 @@ class BackendClient implements BackendClientInterface {
     $indexId = $this->getIndexId($index);
     try {
       $params = $this->fieldParamsBuilder->mapFieldParams($indexId, $index);
+      if ($this->checkFieldMapping($index, $params['body']['properties'])) {
+        $index->clear();
+      }
       $this->client->indices()->putMapping($params);
     }
     catch (OpenSearchException $e) {
@@ -298,6 +300,43 @@ class BackendClient implements BackendClientInterface {
     }
   }
 
+  /**
+   * Check if field mapping has changed.
+   *
+   * @param \Drupal\search_api\IndexInterface $index
+   *   The index.
+   * @param array $properties
+   *   The array of field mapping properties.
+   *
+   * @return bool
+   *   Returns TRUE or FALSE.
+   */
+  protected function checkFieldMapping(IndexInterface $index, array $properties): bool {
+    $indexId = $this->getIndexId($index);
+    $mapping = $this->client->indices()->getMapping(['index' => $indexId]);
+
+    // Missing original properties mapping.
+    if (!isset($mapping[$indexId]['mappings']['properties'])) {
+      return TRUE;
+    }
+
+    // Property has been added or removed.
+    if (array_diff_key($properties, $mapping[$indexId]['mappings']['properties'])) {
+      return TRUE;
+    }
+
+    // Properties have changed or are missing.
+    foreach ($properties as $name => $property) {
+      foreach ($mapping[$indexId]['mappings']['properties'][$name] as $key => $value) {
+        if (!isset($property[$key]) || $property[$key] !== $value) {
+          return TRUE;
+        }
+      }
+    }
+
+    return FALSE;
+  }
+
   /**
    * {@inheritdoc}
    */