Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/book/src/BookUninstallValidator.php

@@ -0,0 +1,98 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\book\BookUninstallValidator.
+ */
+
+namespace Drupal\book;
+
+use Drupal\Core\Entity\Query\QueryFactory;
+use Drupal\Core\Extension\ModuleUninstallValidatorInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslationInterface;
+
+/**
+ * Prevents book module from being uninstalled whilst any book nodes exist or
+ * there are any book outline stored.
+ */
+class BookUninstallValidator implements ModuleUninstallValidatorInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The book outline storage.
+   *
+   * @var \Drupal\book\BookOutlineStorageInterface
+   */
+  protected $bookOutlineStorage;
+
+  /**
+   * The entity query for node.
+   *
+   * @var \Drupal\Core\Entity\Query\QueryInterface
+   */
+  protected $entityQuery;
+
+  /**
+   * Constructs a new BookUninstallValidator.
+   *
+   * @param \Drupal\book\BookOutlineStorageInterface $book_outline_storage
+   *   The book outline storage.
+   * @param \Drupal\Core\Entity\Query\QueryFactory $query_factory
+   *   The entity query factory.
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   The string translation service.
+   */
+  public function __construct(BookOutlineStorageInterface $book_outline_storage, QueryFactory $query_factory, TranslationInterface $string_translation) {
+    $this->bookOutlineStorage = $book_outline_storage;
+    $this->entityQuery = $query_factory->get('node');
+    $this->stringTranslation = $string_translation;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($module) {
+    $reasons = [];
+    if ($module == 'book') {
+      if ($this->hasBookOutlines()) {
+        $reasons[] = $this->t('To uninstall Book, delete all content that is part of a book');
+      }
+      else {
+        // The book node type is provided by the Book module. Prevent uninstall
+        // if there are any nodes of that type.
+        if ($this->hasBookNodes()) {
+          $reasons[] = $this->t('To uninstall Book, delete all content that has the Book content type');
+        }
+      }
+    }
+    return $reasons;
+  }
+
+  /**
+   * Checks if there are any books in an outline.
+   *
+   * @return bool
+   *   TRUE if there are books, FALSE if not.
+   */
+  protected function hasBookOutlines() {
+    return $this->bookOutlineStorage->hasBooks();
+  }
+
+  /**
+   * Determines if there is any book nodes or not.
+   *
+   * @return bool
+   *   TRUE if there are book nodes, FALSE otherwise.
+   */
+  protected function hasBookNodes() {
+    $nodes = $this->entityQuery
+      ->condition('type', 'book')
+      ->accessCheck(FALSE)
+      ->range(0, 1)
+      ->execute();
+    return !empty($nodes);
+  }
+
+}