MC-18948: Switch default search engine from MySQL to ElasticSearch

- fixing admin to default to search engine if not valid

Author: cpartica

app/code/Magento/CatalogSearch/Model/Adminhtml/System/Config/Backend/Engine.php

@@ -5,6 +5,8 @@
  */
 namespace Magento\CatalogSearch\Model\Adminhtml\System\Config\Backend;
 
+use Magento\Framework\App\ObjectManager;
+
 /**
  * Backend model for catalog search engine system config
  *
@@ -18,6 +20,11 @@ class Engine extends \Magento\Framework\App\Config\Value
      */
     protected $indexerRegistry;
 
+    /**
+     * @var \Magento\Framework\Search\EngineResolverInterface
+     */
+    private $engineResolver;
+
     /**
      * @param \Magento\Framework\Model\Context $context
      * @param \Magento\Framework\Registry $registry
@@ -27,6 +34,7 @@ class Engine extends \Magento\Framework\App\Config\Value
      * @param \Magento\Framework\Model\ResourceModel\AbstractResource $resource
      * @param \Magento\Framework\Data\Collection\AbstractDb $resourceCollection
      * @param array $data
+     * @param \Magento\Framework\Search\EngineResolverInterface|null $engineResolver
      */
     public function __construct(
         \Magento\Framework\Model\Context $context,
@@ -36,12 +44,29 @@ public function __construct(
         \Magento\Framework\Indexer\IndexerRegistry $indexerRegistry,
         \Magento\Framework\Model\ResourceModel\AbstractResource $resource = null,
         \Magento\Framework\Data\Collection\AbstractDb $resourceCollection = null,
-        array $data = []
+        array $data = [],
+        \Magento\Framework\Search\EngineResolverInterface $engineResolver = null
     ) {
         $this->indexerRegistry = $indexerRegistry;
+        $this->engineResolver = $engineResolver
+            ?? ObjectManager::getInstance()->get(\Magento\Framework\Search\EngineResolverInterface::class);
         parent::__construct($context, $registry, $config, $cacheTypeList, $resource, $resourceCollection, $data);
     }
 
+    /**
+     * @inheritDoc
+     */
+    public function beforeSave()
+    {
+        parent::beforeSave();
+        $value = (string)$this->getValue();
+        if (empty($value)) {
+            $defaultCountry = $this->engineResolver->getCurrentSearchEngine();
+            $this->setValue($defaultCountry);
+        }
+        return $this;
+    }
+
     /**
      * After save call
      *

app/code/Magento/CatalogSearch/etc/adminhtml/system.xml

@@ -18,6 +18,7 @@
                 <label>Catalog Search</label>
                 <field id="engine" canRestore="1">
                     <backend_model>Magento\CatalogSearch\Model\Adminhtml\System\Config\Backend\Engine</backend_model>
+                    <comment>If not specified, Default Search Engine will be used.</comment>
                 </field>
                 <field id="min_query_length" translate="label comment" type="text" sortOrder="5" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                     <label>Minimal Query Length</label>

app/code/Magento/Search/Model/Adminhtml/System/Config/Source/Engine.php

@@ -5,6 +5,9 @@
  */
 namespace Magento\Search\Model\Adminhtml\System\Config\Source;
 
+use Magento\Framework\App\ObjectManager;
+use Magento\Framework\Search\EngineResolverInterface;
+
 /**
  * All registered search adapters
  *
@@ -21,23 +24,34 @@ class Engine implements \Magento\Framework\Option\ArrayInterface
     private $engines;
 
     /**
-     * Construct
+     * Engine Resolver
      *
+     * @var EngineResolverInterface
+     */
+    private $engineResolver;
+
+    /**
      * @param array $engines
+     * @param EngineResolverInterface|null $engineResolver
      */
     public function __construct(
-        array $engines
+        array $engines,
+        EngineResolverInterface $engineResolver = null
     ) {
         $this->engines = $engines;
+        $this->engineResolver = $engineResolver ?? ObjectManager::getInstance()->get(EngineResolverInterface::class);
     }
 
     /**
-     * {@inheritdoc}
+     * @inheritdoc
      */
     public function toOptionArray()
     {
-        $options = [];
+        $options = [['value' => null, 'label' => __('--Please Select--')]];
         foreach ($this->engines as $key => $label) {
+            if ($this->engineResolver->getCurrentSearchEngine() === $key) {
+                $label = $label . ' ' . __('Default');
+            }
             $options[] = ['value' => $key, 'label' => $label];
         }
         return $options;