wikimedia/mediawiki-extensions-Wikibase

<?php

declare( strict_types=1 );
namespace Wikibase\Lib\Store\Sql\Terms;

use Wikimedia\Rdbms\IDatabase;

/**
 * Trait for code-sharing method for finding unused terms based on the "NN_term_in_lang_id" relation
 *
 * @see @ref docs_storage_terms
 * @license GPL-2.0-or-later
 */
trait FindUnusedTermTrait {

    /**
     * Of the given term in lang IDs, find those that aren’t used by any other items or properties.
     *
     * Currently, this does not account for term in lang IDs that may be used anywhere else,
     * e.g. by other entity types; anyone who uses term in lang IDs elsewhere runs the risk
     * of those terms being deleted at any time. This may be improved in the future.
     *
     * 1) Iterate through the IDs that we have been given and determine if they
     * appear to be used or not in either the property or item term tables.
     * 2) Select FOR UPDATE the rows in the wbt_property_terms and wbt_item_terms
     * tables so they lock and nothing will happen to them.
     *
     * An alternative to this would be immediately lock all $termInLangIds, but that would
     * lead to deadlocks. see T234948
     *
     * @param int[] $termInLangIds (wbtl_id)
     * @param IDatabase $dbw
     * @return int[] wbtl_ids to be cleaned
     */
    private function findActuallyUnusedTermInLangIds( array $termInLangIds, IDatabase $dbw ) {
        $unusedTermInLangIds = [];
        foreach ( $termInLangIds as $termInLangId ) {
            // Note: Not batching here is intentional to avoid deadlocks (see method comment)
            $usedInProperties = $dbw->newSelectQueryBuilder()
                ->select( 'wbpt_term_in_lang_id' )
                ->from( 'wbt_property_terms' )
                ->where( [ 'wbpt_term_in_lang_id' => $termInLangId ] )
                ->caller( __METHOD__ )->fetchField();
            $usedInItems = $dbw->newSelectQueryBuilder()
                ->select( 'wbit_term_in_lang_id' )
                ->from( 'wbt_item_terms' )
                ->where( [ 'wbit_term_in_lang_id' => $termInLangId ] )
                ->caller( __METHOD__ )->fetchField();

            if ( $usedInProperties === false && $usedInItems === false ) {
                $unusedTermInLangIds[] = $termInLangId;
            }
        }
        if ( $unusedTermInLangIds === [] ) {
            return [];
        }

        $termInLangIdsUsedInPropertiesSinceLastLoopRan = $dbw->newSelectQueryBuilder()
            ->select( 'wbpt_term_in_lang_id' )
            ->forUpdate()
            ->from( 'wbt_property_terms' )
            ->where( [ 'wbpt_term_in_lang_id' => $unusedTermInLangIds ] )
            ->caller( __METHOD__ )->fetchFieldValues();
        $termInLangIdsUsedInItemsSinceLastLoopRan = $dbw->newSelectQueryBuilder()
            ->select( 'wbit_term_in_lang_id' )
            ->forUpdate()
            ->from( 'wbt_item_terms' )
            ->where( [ 'wbit_term_in_lang_id' => $unusedTermInLangIds ] )
            ->caller( __METHOD__ )->fetchFieldValues();

        $finalUnusedTermInLangIds = array_diff(
            $unusedTermInLangIds,
            $termInLangIdsUsedInPropertiesSinceLastLoopRan,
            $termInLangIdsUsedInItemsSinceLastLoopRan
        );

        return $finalUnusedTermInLangIds;
    }

}