class RowPluginBase

abstract class RowPluginBase extends PluginBase {
    
    /**
     * {@inheritdoc}
     */
    protected $usesOptions = TRUE;
    
    /**
     * Does the row plugin support to add fields to its output.
     *
     * @var bool
     */
    protected $usesFields = FALSE;
    
    /**
     * Returns the usesFields property.
     *
     * @return bool
     */
    public function usesFields() {
        return $this->usesFields;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        if (isset($this->base_table)) {
            $options['relationship'] = [
                'default' => 'none',
            ];
        }
        return $options;
    }
    
    /**
     * Provide a form for setting options.
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        if (isset($this->base_table)) {
            $executable = $form_state->get('view')
                ->getExecutable();
            // A whole bunch of code to figure out what relationships are valid for
            // this item.
            $relationships = $executable->display_handler
                ->getOption('relationships');
            $relationship_options = [];
            foreach ($relationships as $relationship) {
                $relationship_handler = Views::handlerManager('relationship')->getHandler($relationship);
                // If this relationship is valid for this type, add it to the list.
                $data = Views::viewsData()->get($relationship['table']);
                $base = $data[$relationship['field']]['relationship']['base'];
                if ($base == $this->base_table) {
                    $relationship_handler->init($executable, $relationship);
                    $relationship_options[$relationship['id']] = $relationship_handler->adminLabel();
                }
            }
            if (!empty($relationship_options)) {
                $relationship_options = array_merge([
                    'none' => $this->t('Do not use a relationship'),
                ], $relationship_options);
                $rel = empty($this->options['relationship']) ? 'none' : $this->options['relationship'];
                if (empty($relationship_options[$rel])) {
                    // Pick the first relationship.
                    $rel = key($relationship_options);
                }
                $form['relationship'] = [
                    '#type' => 'select',
                    '#title' => $this->t('Relationship'),
                    '#options' => $relationship_options,
                    '#default_value' => $rel,
                ];
            }
            else {
                $form['relationship'] = [
                    '#type' => 'value',
                    '#value' => 'none',
                ];
            }
        }
    }
    
    /**
     * Validate the options form.
     */
    public function validateOptionsForm(&$form, FormStateInterface $form_state) {
    }
    
    /**
     * Perform any necessary changes to the form values prior to storage.
     * There is no need for this function to actually store the data.
     */
    public function submitOptionsForm(&$form, FormStateInterface $form_state) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        if (isset($this->base_table)) {
            if (isset($this->options['relationship']) && isset($this->view->relationship[$this->options['relationship']])) {
                $relationship = $this->view->relationship[$this->options['relationship']];
                $this->field_alias = $this->view->query
                    ->addField($relationship->alias, $this->base_field);
            }
            else {
                $this->field_alias = $this->view->query
                    ->addField($this->base_table, $this->base_field);
            }
        }
    }
    
    /**
     * Allow the style to do stuff before each row is rendered.
     *
     * @param $result
     *   The full array of results from the query.
     */
    public function preRender($result) {
    }
    
    /**
     * Render a row object. This usually passes through to a theme template
     * of some form, but not always.
     *
     * @param object $row
     *   A single row of the query result, so an element of $view->result.
     *
     * @return string
     *   The rendered output of a single row, used by the style plugin.
     */
    public function render($row) {
        return [
            '#theme' => $this->themeFunctions(),
            '#view' => $this->view,
            '#options' => $this->options,
            '#row' => $row,
            '#field_alias' => isset($this->field_alias) ? $this->field_alias : '',
        ];
    }

}