Views custom filter

Sometimes out-of-the-box views functionality does not enough or the logic of the application very specific.

For instants, we have to create a custom filter. Well, let's have a look how to create a custom view's filter.

First of all, let's create a module with the structure like this:

dw_view_filter
├── src
│   └── Plugin
│       └── views
│           └── filter
│               └── ExampleViewsFilter.php
├── dw_view_filter.info.yml
└── dw_view_filter.views.inc

File dw_view_filter.views.inc content:

<?php

/**
 * Implements hook_views_data_alter().
 */
function dw_view_filter_views_data_alter(array &$data): void {
  $data['node_field_data']['example_date_filter'] = [
    'title' => t('Example date filter'),
    'filter' => [
      'title' => t('Example date filter'),
      'help' => t('Example date filter'),
      'field' => 'nid',
      'id' => 'example_date_filter'
    ],
  ];
}

File dw_view_filter.info.yml content:

name: 'View Filter'
type: module
description: 'This module provides example of custom view filter.'
core_version_requirement: ^9
package: 'Drupal Way'
dependencies:
  - drupal:views
  - drupal:node

File ExampleViewsFilter.php content:

<?php

namespace Drupal\dw_view_filter\Plugin\views\filter;

use Drupal\views\Annotation\ViewsFilter;
use Drupal\views\Plugin\views\filter\FilterPluginBase;
use Drupal\views\Plugin\ViewsHandlerManager;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Drupal\Core\Datetime\DrupalDateTime;

/**
 * Field handler to example data filter.
 *
 * @ingroup views_field_handlers
 *
 * @ViewsFilter("example_date_filter")
 */
class ExampleViewsFilter extends FilterPluginBase {

  /**
   * Views Handler Plugin Manager.
   *
   * @var \Drupal\views\Plugin\ViewsHandlerManager
   */
  protected ViewsHandlerManager $joinHandler;

  /**
   * ExampleViewsFilter constructor.
   *
   * @param array $configuration
   * @param $plugin_id
   * @param $plugin_definition
   * @param \Drupal\views\Plugin\ViewsHandlerManager $join_handler
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, ViewsHandlerManager $join_handler) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->joinHandler = $join_handler;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition): ExampleViewsFilter {
    return new static(
      $configuration, $plugin_id, $plugin_definition,
      $container->get('plugin.manager.views.join')
    );
  }

  /**
   * {@inheritdoc}
   */
  public function query(): void {
    $this->ensureMyTable();

    $table = 'node__field_date';
    $join = $this->joinHandler->createInstance('standard', [
      'table' => $table,
      'field' => 'entity_id',
      'left_table' => 'node_field_data',
      'left_field' => 'nid',
    ]);

    $this->query->addRelationship($table, $join, 'node_field_data');
    $this->query->addWhere($this->options['group'], $table . '.field_date_value', (new DrupalDateTime())->format('Y-m-d\TH:i:s'), '<=');
  }
}

The code is filtering nodes with field field_date.

So, a few notes to be more clear:

The field node__field_date is the table of your date field in Manage fields like field_date

Thi is column field_date_value of field_date table

Basically, this is it. But we can improve the filter's logic.

We can add exposed form for this filter and use two option Upcoming and Past:

<?php

use Drupal\Core\Form\FormStateInterface;

/**
 * @param $form
 * @param \Drupal\Core\Form\FormStateInterface $form_state
 */
protected function valueForm(array &$form, FormStateInterface $form_state): void {
  if ($form_state->get('exposed')) {
    $form['value']['example_date_filter'] = [
      '#title' => $this->t('Filter by date'),
      '#type' => 'select',
      '#default_value' => 'past',
      '#options' => [
        'upcoming' => $this->t('Upcoming'),
        'past' => $this->t('Past'),
      ],
    ];
  }
}

And we have to modify function query:

<?php

/**
 * {@inheritdoc}
 */
public function query(): void {
  $this->ensureMyTable();

  $id = $this->options['expose']['identifier'];
  $input = $this->view->getExposedInput();

  $table = 'node__field_date';
  $join = $this->joinHandler->createInstance('standard', [
    'table' => $table,
    'field' => 'entity_id',
    'left_table' => 'node_field_data',
    'left_field' => 'nid',
  ]);

  // Default value for "Past".
  $operator = '<=';

  if (isset($input[$id]) && $input[$id] === 'past') {
    $operator = '<=';
  }

  if (isset($input[$id]) && $input[$id] === 'upcoming') {
    $operator = '>=';
  }

  $this->query->addRelationship($table, $join, 'node_field_data');
  $this->query->addWhere($this->options['group'], $table . '.field_date_value', (new DrupalDateTime())->format('Y-m-d\TH:i:s'), $operator);
}