Add example for how to expose custom entity to Group module

advertiser.module

@@ -0,0 +1,12 @@
+<?php
+
+use Drupal\group\Entity\Group;
+
+
+function _advertiser_show_adding_to_group() {
+  // Make sure you have added an Advertiser and a Group
+  $ad = \Drupal\advertiser\Entity\Advertiser::load(1);
+  $group = Group::load(1);
+
+  $group->addContent($ad, 'advertiser:advertiser');
+}

src/Plugin/GroupContentEnabler/AdvertiserEntity.php

@@ -0,0 +1,99 @@
+<?php
+
+namespace Drupal\advertiser\Plugin\GroupContentEnabler;
+
+use Drupal\group\Entity\GroupInterface;
+use Drupal\group\Plugin\GroupContentEnablerBase;
+use Drupal\node\Entity\NodeType;
+use Drupal\Core\Url;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Provides a content enabler for nodes.
+ *
+ * @GroupContentEnabler(
+ *   id = "advertiser",
+ *   label = @Translation("Advertiser"),
+ *   description = @Translation("Adds advertisers to groups."),
+ *   entity_type_id = "advertiser",
+ *   entity_access = TRUE,
+ *   pretty_path_key = "node",
+ *   reference_label = @Translation("Title"),
+ *   reference_description = @Translation("The name of the advertiser to add to the group"),
+ *   deriver = "Drupal\advertiser\Plugin\GroupContentEnabler\AdvertiserEntityDeriver"
+ * )
+ */
+class AdvertiserEntity extends GroupContentEnablerBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getGroupOperations(GroupInterface $group) {
+    $account = \Drupal::currentUser();
+    $plugin_id = $this->getPluginId();
+    $type = $this->getEntityBundle();
+    $operations = [];
+
+    if ($group->hasPermission("create $plugin_id entity", $account)) {
+      $route_params = ['group' => $group->id(), 'plugin_id' => $plugin_id];
+      $operations["advertiser-create-$type"] = [
+        'title' => $this->t('Create @type', ['@type' => 'advertiser']),
+        'url' => new Url('entity.group_content.create_form', $route_params),
+        'weight' => 30,
+      ];
+    }
+
+    return $operations;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getTargetEntityPermissions() {
+    $permissions = parent::getTargetEntityPermissions();
+    $plugin_id = $this->getPluginId();
+
+    // Add a 'view unpublished' permission by re-using most of the 'view' one.
+    $original = $permissions["view $plugin_id entity"];
+    $permissions["view unpublished $plugin_id entity"] = [
+      'title' => str_replace('View ', 'View unpublished ', $original['title']),
+    ] + $original;
+
+    return $permissions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    $config = parent::defaultConfiguration();
+    $config['entity_cardinality'] = 1;
+    return $config;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    $form = parent::buildConfigurationForm($form, $form_state);
+
+    // Disable the entity cardinality field as the functionality of this module
+    // relies on a cardinality of 1. We don't just hide it, though, to keep a UI
+    // that's consistent with other content enabler plugins.
+    $info = $this->t("This field has been disabled by the plugin to guarantee the functionality that's expected of it.");
+    $form['entity_cardinality']['#disabled'] = TRUE;
+    $form['entity_cardinality']['#description'] .= '<br /><em>' . $info . '</em>';
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function calculateDependencies() {
+    $dependencies = parent::calculateDependencies();
+    $dependencies['config'][] = 'node.type.' . $this->getEntityBundle();
+    return $dependencies;
+  }
+
+}

src/Plugin/GroupContentEnabler/AdvertiserEntityDeriver.php

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+<?php
+
+namespace Drupal\advertiser\Plugin\GroupContentEnabler;
+
+use Drupal\node\Entity\NodeType;
+use Drupal\Component\Plugin\Derivative\DeriverBase;
+
+class AdvertiserEntityDeriver extends DeriverBase {
+
+  /**
+   * {@inheritdoc}.
+   */
+  public function getDerivativeDefinitions($base_plugin_definition) {
+//    foreach (NodeType::loadMultiple() as $name => $node_type) {
+//      $label = $node_type->label();
+//      $this->derivatives[$name] = [
+//        'entity_bundle' => $name,
+//        'label' => t('Group node') . " ($label)",
+//        'description' => t('Adds %type content to groups both publicly and privately.', ['%type' => $label]),
+//      ] + $base_plugin_definition;
+//    }
+//
+//    return $this->derivatives;
+
+    $this->derivatives['advertiser'] = [
+        'entity_bundle' => 'advertiser',
+        'label' => t('Group content: Advertiser'),
+        'description' => t('Adds advertiser content to groups both publicly and privately.'),
+      ] + $base_plugin_definition;
+
+    return $this->derivatives;
+
+  }
+
+}