@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace Drupal\foo\Entity;
 
 use Drupal\Core\Config\Entity\ConfigEntityBundleBase;
+use Drupal\Core\Plugin\DefaultSingleLazyPluginCollection;
 
 /**
  * Provides the Booking Unit Type entity.
@@ -39,6 +40,8 @@ use Drupal\Core\Config\Entity\ConfigEntityBundleBase;
  *   config_export = {
  *     "id",
  *     "label",
+ *     "foo_type",
+ *     "foo_type_config",
  *   },
  *   links = {
  *     "add-form" = "/admin/structure/foo_unit_type/add",

    */
   protected $label = '';
 
+  /**
+   * The foo type plugin ID.
+   *
+   * @var string
+   */
+  protected $foo_type = '';
+
+  /**
+   * The foo type plugin configuration.
+   *
+   * @var array
+   */
+  protected $foo_type_config = [];
+
+  /**
+   * The plugin collection that holds the foo type plugin for this entity.
+   *
+   * @var \Drupal\Component\Plugin\DefaultSingleLazyPluginCollection
+   */
+  protected $fooPluginCollection;
+
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPluginCollections() {
+    return [
+      'foo_type_config' => $this->getBookingTypePluginCollection(),
+    ];
+  }
+
+  /**
+   * Encapsulates the creation of the foo type plugin collection.
+   *
+   * @return \Drupal\Component\Plugin\DefaultSingleLazyPluginCollection
+   *   The plugin collection.
+   */
+  protected function getBookingTypePluginCollection() {
+    if (!$this->fooPluginCollection) {
+      $this->fooPluginCollection = new DefaultSingleLazyPluginCollection(
+        \Drupal::service('plugin.manager.foo_type'),
+        $this->foo_type,
+        $this->foo_type_config,
+      );
+    }
+    return $this->fooPluginCollection;
+  }
+
 }

     label:
       type: label
       label: Name
+    foo_type:
+      type: string
+      label: Foo type
+    foo_type_config:
+      type: foo.foo_availability.plugin.[%parent.content_plugin]
+      label: 'Foo configuration'
+
+# Schema for foo type content plugins.
+foo.foo_availability.plugin.*:
+  type: mapping
+  label: 'Foo type configuration'