Issue #3178599 by mglaman, jsacksick: Provide a computed field for accessing the default variation

modules/product/src/Entity/Product.php

@@ -6,6 +6,7 @@ use Drupal\commerce\Entity\CommerceContentEntityBase;
 use Drupal\commerce\EntityOwnerTrait;
 use Drupal\commerce_product\Event\ProductDefaultVariationEvent;
 use Drupal\commerce_product\Event\ProductEvents;
+use Drupal\commerce_product\Plugin\Field\ComputedDefaultVariation;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Entity\EntityPublishedTrait;
 use Drupal\Core\Entity\EntityChangedTrait;
@@ -378,6 +379,17 @@ class Product extends CommerceContentEntityBase implements ProductInterface {
       ->setDisplayConfigurable('form', TRUE)
       ->setDisplayConfigurable('view', TRUE);
 
+    $fields['default_variation'] = BaseFieldDefinition::create('entity_reference')
+      ->setLabel(t('Default variation'))
+      ->setDescription(t('The default variation.'))
+      ->setSetting('target_type', 'commerce_product_variation')
+      ->setSetting('handler', 'default')
+      ->setComputed(TRUE)
+      ->setCardinality(1)
+      ->setClass(ComputedDefaultVariation::class)
+      ->setDisplayConfigurable('form', FALSE)
+      ->setDisplayConfigurable('view', FALSE);
+
     $fields['path'] = BaseFieldDefinition::create('path')
       ->setLabel(t('URL alias'))
       ->setDescription(t('The product URL alias.'))
@@ -426,6 +438,7 @@ class Product extends CommerceContentEntityBase implements ProductInterface {
     /** @var \Drupal\Core\Field\BaseFieldDefinition[] $fields */
     $fields = [];
     $fields['variations'] = clone $base_field_definitions['variations'];
+    $fields['default_variation'] = clone $base_field_definitions['default_variation'];
     /** @var \Drupal\commerce_product\Entity\ProductTypeInterface $product_type */
     $product_type = ProductType::load($bundle);
     if ($product_type) {
@@ -434,6 +447,9 @@ class Product extends CommerceContentEntityBase implements ProductInterface {
       $fields['variations']->setSetting('handler_settings', [
         'target_bundles' => [$variation_type_id => $variation_type_id],
       ]);
+      $fields['default_variation']->setSetting('handler_settings', [
+        'target_bundles' => [$variation_type_id => $variation_type_id],
+      ]);
     }
 
     return $fields;

modules/product/src/Plugin/Field/ComputedDefaultVariation.php

+<?php
+
+namespace Drupal\commerce_product\Plugin\Field;
+
+use Drupal\commerce_product\Entity\ProductInterface;
+use Drupal\Core\Field\EntityReferenceFieldItemList;
+use Drupal\Core\TypedData\ComputedItemListTrait;
+
+/**
+ * Computed field item list for the default_variation field.
+ */
+class ComputedDefaultVariation extends EntityReferenceFieldItemList {
+  use ComputedItemListTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function computeValue() {
+    $product = $this->getEntity();
+    assert($product instanceof ProductInterface);
+    $this->list[0] = $this->createItem(0, $product->getDefaultVariation());
+  }
+
+}

modules/product/tests/src/Kernel/Entity/ProductTest.php

@@ -163,6 +163,7 @@ class ProductTest extends CommerceKernelTestBase {
     $this->assertNotEmpty($product->hasVariation($variation1));
 
     $this->assertEquals($product->getDefaultVariation(), $variation2);
+    $this->assertEquals($variation2, $product->get('default_variation')->entity);
     $this->assertNotEquals($product->getDefaultVariation(), $variation1);
 
     // Confirm that postSave() sets the product_id on each variation.