Drupal 8 模块开发 7.2 ： 加载字段的例子

原文地址：
https://docs.acquia.com/articles/drupal-8-loading-fields-examples  
 

例子模块

我们将创建一个例子模块，加载一个节点（node），输出它的一些信息。首先，至少创建一个节点，body 字段填写一些内容。然后，我们创建这个模块，加载单一节点。  

创建文件 field_example.info.yml ：

name: Field Example
type: module
description: Example showing how to use fields
core: 8.x
package: Examples

创建文件 field_example.routing.yml :

field_example.simple:
  path: 'examples/field-example/simple'
  defaults:
    _controller: '\Drupal\field_example\Controller\FieldExampleDefaultController::simple'
  requirements:
    _access: 'TRUE'

创建控制器文件 src/Controller/FieldExampleDefaultController.php ：

下载文件

<?php

/**
 * @file
 * Contains \Drupal\field_example\Controller\FieldExampleDefaultController.
 */

namespace Drupal\field_example\Controller;

use Drupal\Core\Controller\ControllerBase;
use Drupal\Core\Entity\EntityManagerInterface;
use Drupal\Core\Entity\Query\QueryFactory;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Controller routines for field example routes.
 */
class FieldExampleDefaultController extends ControllerBase {

  /**
   * @var \Drupal\Core\Entity\EntityManagerInterface
   */
  protected $entityManager;

  /**
   * @var \Drupal\Core\Entity\Query\QueryFactory
   */
  protected $queryFactory;

  /**
   * @param \Drupal\Core\Entity\EntityManagerInterface $entityManager
   * @param \Drupal\Core\Entity\Query\QueryFactory $queryFactory
   */
  public function __construct(EntityManagerInterface $entityManager, QueryFactory $queryFactory) {
    $this->entityManager = $entityManager;
    $this->queryFactory = $queryFactory;

  }

  /**
   * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
   * @return static
   */
  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('entity.manager'),
      $container->get('entity.query')
    );
  }

  public function simple() {
    /**
     * We need to get one node with a body field.
     */

    /**
     * @var $query \Drupal\Core\Entity\Query\QueryInterface
     */
    $query = $this->queryFactory->get('node');

    // We just want some nodes.
    $nids = $query->execute();

    // If there are no nodes, we exit.
    if (count($nids) < 1) {
      return ['#markup' => $this->t('No nodes with a body field.')];
    }

    /**
     * @var $entity_storage \Drupal\Core\Entity\ContentEntityStorageBase
     */
    $entity_storage = $this->entityManager->getStorage('node');

    /**
     * @var $entity \Drupal\Core\Entity\Entity
     */
    $entity = $entity_storage->load(array_values($nids)[0]);

    // We will get the values from here.

    return [
      '#markup' => 'placeholder',
    ];
  }
}

创建节点后，我们来取得 body 字段的值，并使用之前讲到的方式改变它。

/**
 * @var $field \Drupal\Core\Field\FieldItemList
 */
$body_field = $entity->get('body');

// If we want a value off the first item, we can use a magic method __get()
// Which is sometimes easier to use.
$simple_value = $body_field->value;

// We get a array of items for this field.
// Unlike Drupal 7, there are no language keys.
$field_value = $body_field->getValue();

// We will set the summary to the value.
// We don't need to update the entity because the field setValue does that already.
$body_field->summary = $body_field->value;

// or
$field_value[0]['summary'] = $field_value[0]['value'];
$body_field->setValue($field_value);

/**
 * @var $definition \Drupal\Core\Field\BaseFieldDefinition
 */
$definition = $body_field->getFieldDefinition();

$field_type = $definition->get('field_type');

return [
  'field_type' => [
    '#markup' => 'Field Type: ' . $field_type,
    '#theme_wrappers' => [
      'container' => [],
    ],
  ],
  'field_value' => [
    '#markup' => 'Field Value: ' . $body_field->value,
    '#theme_wrappers' => [
      'container' => [],
    ],
  ],
];

回顾

我们学习了长、短两种访问、编辑字段的方法。从 Drupal 7 的主要变化是我们不再直接访问字段，而是要通过实体访问字段。另外现在统一使用 FieldItemList 访问字段。

某些情况下，你需要访问 field 对象的 Field Storage 系统。