class RelationshipPluginBase

abstract class RelationshipPluginBase extends HandlerBase {
    
    /**
     * The relationship alias.
     *
     * @var string
     */
    public $alias;
    
    /**
     * Overrides \Drupal\views\Plugin\views\HandlerBase::init().
     *
     * Init handler to let relationships live on tables other than
     * the table they operate on.
     */
    public function init(ViewExecutable $view, DisplayPluginBase $display, array &$options = NULL) {
        parent::init($view, $display, $options);
        if (isset($this->definition['relationship table'])) {
            $this->table = $this->definition['relationship table'];
        }
        if (isset($this->definition['relationship field'])) {
            // Set both realField and field so custom handler can rely on the old
            // field value.
            $this->realField = $this->field = $this->definition['relationship field'];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function usesGroupBy() {
        return FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        // Relationships definitions should define a default label, but if they
        // aren't get another default value.
        if (!empty($this->definition['label'])) {
            // Cast the label to a string since it is an object.
            // @see \Drupal\Core\StringTranslation\TranslatableMarkup
            $label = (string) $this->definition['label'];
        }
        else {
            $label = !empty($this->definition['field']) ? $this->definition['field'] : $this->definition['base field'];
        }
        $options['admin_label']['default'] = $label;
        $options['required'] = [
            'default' => FALSE,
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        unset($form['admin_label']['#fieldset']);
        $form['admin_label']['#weight'] = -1;
        $form['required'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Require this relationship'),
            '#description' => $this->t('Enable to hide items that do not contain this relationship'),
            '#default_value' => !empty($this->options['required']),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        if (!empty($this->definition['deprecated'])) {
            @trigger_error($this->definition['deprecated'], E_USER_DEPRECATED);
        }
        // Figure out what base table this relationship brings to the party.
        $table_data = Views::viewsData()->get($this->definition['base']);
        $base_field = empty($this->definition['base field']) ? $table_data['table']['base']['field'] : $this->definition['base field'];
        $this->ensureMyTable();
        $def = $this->definition;
        $def['table'] = $this->definition['base'];
        $def['field'] = $base_field;
        $def['left_table'] = $this->tableAlias;
        $def['left_field'] = $this->realField;
        $def['adjusted'] = TRUE;
        if (!empty($this->options['required'])) {
            $def['type'] = 'INNER';
        }
        if (!empty($this->definition['extra'])) {
            $def['extra'] = $this->definition['extra'];
        }
        if (!empty($def['join_id'])) {
            $id = $def['join_id'];
        }
        else {
            $id = 'standard';
        }
        $join = Views::pluginManager('join')->createInstance($id, $def);
        // use a short alias for this:
        $alias = $def['table'] . '_' . $this->table;
        $this->alias = $this->query
            ->addRelationship($alias, $join, $this->definition['base'], $this->relationship);
        // Add access tags if the base table provide it.
        if (empty($this->query->options['disable_sql_rewrite']) && isset($table_data['table']['base']['access query tag'])) {
            $access_tag = $table_data['table']['base']['access query tag'];
            $this->query
                ->addTag($access_tag);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function calculateDependencies() {
        $dependencies = parent::calculateDependencies();
        // Add the provider of the relationship's base table to the dependencies.
        $table_data = $this->getViewsData()
            ->get($this->definition['base']);
        $dependencies['module'][] = $table_data['table']['provider'];
        return $dependencies;
    }

}