Custom field handler

20. Custom Field Handler

When to Use

When you need custom field output: computed values, external API data, complex formatting that can't be achieved with field templates or rewrite rules.

Steps

1. Create handler class — Place in src/Plugin/views/field/MyCustomField.php

   namespace Drupal\mymodule\Plugin\views\field;
   
   use Drupal\views\Plugin\views\field\FieldPluginBase;
   use Drupal\views\Attribute\ViewsField;
   use Drupal\views\ResultRow;
   
   #[ViewsField("my_custom_field")]
   class MyCustomField extends FieldPluginBase {
     public function render(ResultRow $values) {
       $value = $this->getValue($values);
       return ['#markup' => strtoupper($value)];
     }
   }
   

2. Integrate with hook_views_data() — In mymodule.views.inc

   function mymodule_views_data() {
     $data['node_field_data']['custom_title_upper'] = [
       'title' => t('Title (Uppercase)'),
       'field' => ['id' => 'my_custom_field'],
     ];
     return $data;
   }
   

3. Add options form (optional) — For configurable fields

   protected function defineOptions() {
     $options = parent::defineOptions();
     $options['prefix'] = ['default' => ''];
     return $options;
   }
   
   public function buildOptionsForm(&$form, FormStateInterface $form_state) {
     $form['prefix'] = [
       '#type' => 'textfield',
       '#title' => t('Prefix'),
       '#default_value' => $this->options['prefix'],
     ];
     parent::buildOptionsForm($form, $form_state);
   }
   

4. Implement query() for computed fields — Add fields to query

   public function query() {
     $this->ensureMyTable();
     $this->addAdditionalFields(['title', 'status']);
   }
   

Decision Points

At this step...	If...	Then...
render()	Returning HTML	Use render array with #markup, never raw strings
query()	Field pulls from DB	Call ensureMyTable() and addAdditionalFields()
query()	Field is purely computed	Skip query() — no DB fields needed
options form	Field needs config	Override defineOptions() and buildOptionsForm()

Common Mistakes

• Returning string from render() → Return render array; Views expects renderable output
• Not calling ensureMyTable() in query() → Table may not be joined, query fails
• Putting business logic in render() → Keep render() light; extract complex logic to services injected via create()
• Not sanitizing output → Use #markup with trusted content or #plain_text for user input
• Forgetting getValue($values) → Access row data via getValue(), not direct property access

See Also

• Section 29: Views Data Integration — registering fields in hook_views_data()
• Reference: core/modules/views/src/Plugin/views/field/FieldPluginBase.php
• Reference: core/modules/node/src/Plugin/views/field/Node.php — real-world example