GroupwiseMax.php

<?php

namespace Drupal\views\Plugin\views\relationship;

use Drupal\Core\Database\Query\AlterableInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\views\Views;
use Drupal\views\Entity\View;

/**
 * The relationship handler for groupwise maximum queries.
 *
 * It allows a groupwise maximum of the linked in table.
 * For a definition, see:
 * http://dev.mysql.com/doc/refman/5.0/en/example-maximum-column-group-row.html
 * In lay terms, instead of joining to get all matching records in the linked
 * table, we get only one record, a 'representative record' picked according
 * to a given criteria.
 *
 * Example:
 * Suppose we have a term view that gives us the terms: Horse, Cat, Aardvark.
 * We wish to show for each term the most recent node of that term.
 * What we want is some kind of relationship from term to node.
 * But a regular relationship will give us all the nodes for each term,
 * giving the view multiple rows per term. What we want is just one
 * representative node per term, the node that is the 'best' in some way:
 * eg, the most recent, the most commented on, the first in alphabetical order.
 *
 * This handler gives us that kind of relationship from term to node.
 * The method of choosing the 'best' implemented with a sort
 * that the user selects in the relationship settings.
 *
 * So if we want our term view to show the most commented node for each term,
 * add the relationship and in its options, pick the 'Comment count' sort.
 *
 * Relationship definition
 *  - 'outer field': The outer field to substitute into the correlated subquery.
 *       This must be the full field name, not the alias.
 *       Eg: 'term_data.tid'.
 *  - 'argument table',
 *    'argument field': These options define a views argument that the subquery
 *     must add to itself to filter by the main view.
 *     Example: the main view shows terms, this handler is being used to get to
 *     the nodes base table. Your argument must be 'term_node', 'tid', as this
 *     is the argument that should be added to a node view to filter on terms.
 *
 * A note on performance:
 * This relationship uses a correlated subquery, which is expensive.
 * Subsequent versions of this handler could also implement the alternative way
 * of doing this, with a join -- though this looks like it could be pretty messy
 * to implement. This is also an expensive method, so providing both methods and
 * allowing the user to choose which one works fastest for their data might be
 * the best way.
 * If your use of this relationship handler is likely to result in large
 * data sets, you might want to consider storing statistics in a separate table,
 * in the same way as node_comment_statistics.
 *
 * @ingroup views_relationship_handlers
 *
 * @ViewsRelationship("groupwise_max")
 */
class GroupwiseMax extends RelationshipPluginBase {
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['subquery_sort'] = [
            'default' => NULL,
        ];
        // Descending more useful.
        $options['subquery_order'] = [
            'default' => 'DESC',
        ];
        $options['subquery_regenerate'] = [
            'default' => FALSE,
        ];
        $options['subquery_view'] = [
            'default' => FALSE,
        ];
        $options['subquery_namespace'] = [
            'default' => FALSE,
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        // Get the sorts that apply to our base.
        $sorts = Views::viewsDataHelper()->fetchFields($this->definition['base'], 'sort');
        $sort_options = [];
        foreach ($sorts as $sort_id => $sort) {
            $sort_options[$sort_id] = "{$sort['group']}: {$sort['title']}";
        }
        $base_table_data = Views::viewsData()->get($this->definition['base']);
        // Extends the relationship's basic options, allowing the user to pick a
        // sort and an order for it.
        $form['subquery_sort'] = [
            '#type' => 'select',
            '#title' => $this->t('Representative sort criteria'),
            // Provide the base field as sane default sort option.
'#default_value' => !empty($this->options['subquery_sort']) ? $this->options['subquery_sort'] : $this->definition['base'] . '.' . $base_table_data['table']['base']['field'],
            '#options' => $sort_options,
            '#description' => $this->t("The sort criteria is applied to the data brought in by the relationship to determine how a representative item is obtained for each row. For example, to show the most recent node for each user, pick 'Content: Updated date'."),
        ];
        $form['subquery_order'] = [
            '#type' => 'radios',
            '#title' => $this->t('Representative sort order'),
            '#description' => $this->t("The ordering to use for the sort criteria selected above."),
            '#options' => [
                'ASC' => $this->t('Ascending'),
                'DESC' => $this->t('Descending'),
            ],
            '#default_value' => $this->options['subquery_order'],
        ];
        $form['subquery_namespace'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Subquery namespace'),
            '#description' => $this->t('Advanced. Enter a namespace for the subquery used by this relationship.'),
            '#default_value' => $this->options['subquery_namespace'],
        ];
        // WIP: This stuff doesn't work yet: namespacing issues.
        // A list of suitable views to pick one as the subview.
        $views = [
            '' => '- None -',
        ];
        foreach (Views::getAllViews() as $view) {
            // Only get views that are suitable:
            // - base must the base that our relationship joins towards
            // - must have fields.
            if ($view->get('base_table') == $this->definition['base'] && !empty($view->getDisplay('default')['display_options']['fields'])) {
                // TODO: check the field is the correct sort?
                // or let users hang themselves at this stage and check later?
                $views[$view->id()] = $view->id();
            }
        }
        $form['subquery_view'] = [
            '#type' => 'select',
            '#title' => $this->t('Representative view'),
            '#default_value' => $this->options['subquery_view'],
            '#options' => $views,
            '#description' => $this->t('Advanced. Use another view to generate the relationship subquery. This allows you to use filtering and more than one sort. If you pick a view here, the sort options above are ignored. Your view must have the ID of its base as its only field, and should have some kind of sorting.'),
        ];
        $form['subquery_regenerate'] = [
            '#type' => 'checkbox',
            '#title' => $this->t('Generate subquery each time view is run'),
            '#default_value' => $this->options['subquery_regenerate'],
            '#description' => $this->t('Will re-generate the subquery for this relationship every time the view is run, instead of only when these options are saved. Use for testing if you are making changes elsewhere. WARNING: seriously impairs performance.'),
        ];
    }
    
    /**
     * Helper function to create a pseudo view.
     *
     * We use this to obtain our subquery SQL.
     */
    protected function getTemporaryView() {
        $view = View::create([
            'base_table' => $this->definition['base'],
        ]);
        $view->addDisplay('default');
        return $view->getExecutable();
    }
    
    /**
     * When the form is submitted, make sure to clear the subquery string cache.
     */
    public function submitOptionsForm(&$form, FormStateInterface $form_state) {
        $cid = 'views_relationship_groupwise_max:' . $this->view->storage
            ->id() . ':' . $this->view->current_display . ':' . $this->options['id'];
        \Drupal::cache('data')->delete($cid);
    }
    
    /**
     * Generate a subquery given the user options, as set in the options.
     *
     * These are passed in rather than picked up from the object because we
     * generate the subquery when the options are saved, rather than when the view
     * is run. This saves considerable time.
     *
     * @param $options
     *   An array of options:
     *    - subquery_sort: the id of a views sort.
     *    - subquery_order: either ASC or DESC.
     *
     * @return string
     *   The subquery SQL string, ready for use in the main query.
     */
    protected function leftQuery($options) {
        // Either load another view, or create one on the fly.
        if ($options['subquery_view']) {
            $temp_view = Views::getView($options['subquery_view']);
            // Remove all fields from default display
            unset($temp_view->display['default']['display_options']['fields']);
        }
        else {
            // Create a new view object on the fly, which we use to generate a query
            // object and then get the SQL we need for the subquery.
            $temp_view = $this->getTemporaryView();
            // Add the sort from the options to the default display.
            // This is broken, in that the sort order field also gets added as a
            // select field. See https://www.drupal.org/node/844910.
            // We work around this further down.
            $sort = $options['subquery_sort'];
            [
                $sort_table,
                $sort_field,
            ] = explode('.', $sort);
            $sort_options = [
                'order' => $options['subquery_order'],
            ];
            $temp_view->addHandler('default', 'sort', $sort_table, $sort_field, $sort_options);
        }
        // Get the namespace string.
        $temp_view->namespace = !empty($options['subquery_namespace']) ? '_' . $options['subquery_namespace'] : '_INNER';
        $this->subquery_namespace = !empty($options['subquery_namespace']) ? '_' . $options['subquery_namespace'] : 'INNER';
        // The value we add here does nothing, but doing this adds the right tables
        // and puts in a WHERE clause with a placeholder we can grab later.
        $temp_view->args[] = '**CORRELATED**';
        // Add the base table ID field.
        $temp_view->addHandler('default', 'field', $this->definition['base'], $this->definition['field']);
        $relationship_id = NULL;
        // Add the used relationship for the subjoin, if defined.
        if (isset($this->definition['relationship'])) {
            [
                $relationship_table,
                $relationship_field,
            ] = explode(':', $this->definition['relationship']);
            $relationship_id = $temp_view->addHandler('default', 'relationship', $relationship_table, $relationship_field);
        }
        $temp_item_options = [
            'relationship' => $relationship_id,
        ];
        // Add the correct argument for our relationship's base
        // ie the 'how to get back to base' argument.
        // The relationship definition tells us which one to use.
        $temp_view->addHandler('default', 'argument', $this->definition['argument table'], $this->definition['argument field'], $temp_item_options);
        // Build the view. The creates the query object and produces the query
        // string but does not run any queries.
        $temp_view->build();
        // Now take the SelectQuery object the View has built and massage it
        // somewhat so we can get the SQL query from it.
        $subquery = $temp_view->build_info['query'];
        // Workaround until https://www.drupal.org/node/844910 is fixed:
        // Remove all fields from the SELECT except the base id.
        $fields =& $subquery->getFields();
        foreach (array_keys($fields) as $field_name) {
            // The base id for this subquery is stored in our definition.
            if ($field_name != $this->definition['field']) {
                unset($fields[$field_name]);
            }
        }
        // Make every alias in the subquery safe within the outer query by
        // appending a namespace to it, '_inner' by default.
        $tables =& $subquery->getTables();
        foreach (array_keys($tables) as $table_name) {
            $tables[$table_name]['alias'] .= $this->subquery_namespace;
            // Namespace the join on every table.
            if (isset($tables[$table_name]['condition'])) {
                $tables[$table_name]['condition'] = $this->conditionNamespace($tables[$table_name]['condition']);
            }
        }
        // Namespace fields.
        foreach (array_keys($fields) as $field_name) {
            $fields[$field_name]['table'] .= $this->subquery_namespace;
            $fields[$field_name]['alias'] .= $this->subquery_namespace;
        }
        // Namespace conditions.
        $where =& $subquery->conditions();
        $this->alterSubqueryCondition($subquery, $where);
        // Not sure why, but our sort order clause doesn't have a table.
        // TODO: the call to addHandler() above to add the sort handler is probably
        // wrong -- needs attention from someone who understands it.
        // In the meantime, this works, but with a leap of faith.
        $orders =& $subquery->getOrderBy();
        foreach ($orders as $order_key => $order) {
            // But if we're using a whole view, we don't know what we have!
            if ($options['subquery_view']) {
                [
                    $sort_table,
                    $sort_field,
                ] = explode('.', $order_key);
            }
            $orders[$sort_table . $this->subquery_namespace . '.' . $sort_field] = $order;
            unset($orders[$order_key]);
        }
        // The query we get doesn't include the LIMIT, so add it here.
        $subquery->range(0, 1);
        // Extract the SQL the temporary view built.
        $subquery_sql = $subquery->__toString();
        // Replace the placeholder with the outer, correlated field.
        // Eg, change the placeholder ':users_uid' into the outer field 'users.uid'.
        // We have to work directly with the SQL, because putting a name of a field
        // into a SelectQuery that it does not recognize (because it's outer) just
        // makes it treat it as a string.
        $outer_placeholder = ':' . str_replace('.', '_', $this->definition['outer field']);
        $subquery_sql = str_replace($outer_placeholder, $this->definition['outer field'], $subquery_sql);
        return $subquery_sql;
    }
    
    /**
     * Recursive helper to add a namespace to conditions.
     *
     * Similar to _views_query_tag_alter_condition().
     *
     * (Though why is the condition we get in a simple query 3 levels deep???)
     */
    protected function alterSubqueryCondition(AlterableInterface $query, &$conditions) {
        foreach ($conditions as $condition_id => &$condition) {
            // Skip the #conjunction element.
            if (is_numeric($condition_id)) {
                if (is_string($condition['field'])) {
                    $condition['field'] = $this->conditionNamespace($condition['field']);
                }
                elseif (is_object($condition['field'])) {
                    $sub_conditions =& $condition['field']->conditions();
                    $this->alterSubqueryCondition($query, $sub_conditions);
                }
            }
        }
    }
    
    /**
     * Helper function to namespace query pieces.
     *
     * Turns 'foo.bar' into '"foo_NAMESPACE".bar'.
     * PostgreSQL doesn't support mixed-cased identifiers unless quoted, so we
     * need to quote each single part to prevent from query exceptions.
     */
    protected function conditionNamespace($string) {
        $parts = explode(' = ', $string);
        foreach ($parts as &$part) {
            if (strpos($part, '.') !== FALSE) {
                $part = '"' . str_replace('.', $this->subquery_namespace . '".', $part);
            }
        }
        return implode(' = ', $parts);
    }
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        // 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->field;
        $def['adjusted'] = TRUE;
        if (!empty($this->options['required'])) {
            $def['type'] = 'INNER';
        }
        if ($this->options['subquery_regenerate']) {
            // For testing only, regenerate the subquery each time.
            $def['left_query'] = $this->leftQuery($this->options);
        }
        else {
            // Get the stored subquery SQL string.
            $cid = 'views_relationship_groupwise_max:' . $this->view->storage
                ->id() . ':' . $this->view->current_display . ':' . $this->options['id'];
            $cache = \Drupal::cache('data')->get($cid);
            if (isset($cache->data)) {
                $def['left_query'] = $cache->data;
            }
            else {
                $def['left_query'] = $this->leftQuery($this->options);
                \Drupal::cache('data')->set($cid, $def['left_query']);
            }
        }
        if (!empty($def['join_id'])) {
            $id = $def['join_id'];
        }
        else {
            $id = 'subquery';
        }
        $join = Views::pluginManager('join')->createInstance($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);
    }

}