Issue #2934966 by benjifisher, starshaped: Make it easier to get source field...

Issue #2934966 by benjifisher, starshaped: Make it easier to get source field values from media items

core/modules/media/src/MediaSourceBase.php

@@ -319,6 +319,20 @@ protected function getSourceFieldName() {
     return $id;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getSourceFieldValue(MediaInterface $media) {
+    $source_field = $this->configuration['source_field'];
+    if (empty($source_field)) {
+      throw new \RuntimeException('Source field for media source is not defined.');
+    }
+
+    /** @var \Drupal\Core\Field\FieldItemInterface $field_item */
+    $field_item = $media->get($source_field)->first();
+    return $field_item->{$field_item->mainPropertyName()};
+  }
+
   /**
    * {@inheritdoc}
    */

core/modules/media/src/MediaSourceInterface.php

@@ -177,4 +177,18 @@ public function prepareViewDisplay(MediaTypeInterface $type, EntityViewDisplayIn
    */
   public function prepareFormDisplay(MediaTypeInterface $type, EntityFormDisplayInterface $display);
 
+  /**
+   * Get the primary value stored in the source field.
+   *
+   * @param MediaInterface $media
+   *   A media item.
+   *
+   * @return mixed
+   *   The source value.
+   *
+   * @throws \RuntimeException
+   *   If the source field for the media source is not defined.
+   */
+  public function getSourceFieldValue(MediaInterface $media);
+
 }

core/modules/media/tests/src/Kernel/MediaSourceTest.php

@@ -140,6 +140,20 @@ public function testMetadataMapping() {
     $this->assertEquals('Snowball', $media->get($field_name)->value, 'Metadata attribute was not mapped to the field.');
   }
 
+  /**
+   * Tests the getSourceFieldValue() method.
+   */
+  public function testGetSourceFieldValue() {
+    /** @var \Drupal\media\MediaInterface $media */
+    $media = Media::create([
+      'bundle' => $this->testMediaType->id(),
+      'field_media_test' => 'some_value',
+    ]);
+    $media->save();
+    $media_source = $media->getSource();
+    $this->assertSame('some_value', $media_source->getSourceFieldValue($media));
+  }
+
   /**
    * Tests the thumbnail functionality.
    */