DatabaseSqlite.php

Go to the documentation of this file.

<?php
namespace Wikimedia\Rdbms;

use PDO;
use PDOException;
use Exception;
use LockManager;
use FSLockManager;
use InvalidArgumentException;
use RuntimeException;
use stdClass;

class DatabaseSqlite extends Database {
    private static $fulltextEnabled = null;

    protected $dbDir;
    protected $dbPath;
    protected $trxMode;

    protected $lastAffectedRowCount;
    protected $lastResultHandle;

    protected $conn;

    protected $lockMgr;

    private $alreadyAttached = [];

    function __construct( array $p ) {
        if ( isset( $p['dbFilePath'] ) ) {
            $this->dbPath = $p['dbFilePath'];
            $lockDomain = md5( $this->dbPath );
            // Use "X" for things like X.sqlite and ":memory:" for RAM-only DBs
            if ( !isset( $p['dbname'] ) || !strlen( $p['dbname'] ) ) {
                $p['dbname'] = preg_replace( '/\.sqlite\d?$/', '', basename( $this->dbPath ) );
            }
        } elseif ( isset( $p['dbDirectory'] ) ) {
            $this->dbDir = $p['dbDirectory'];
            $lockDomain = $p['dbname'];
        } else {
            throw new InvalidArgumentException( "Need 'dbDirectory' or 'dbFilePath' parameter." );
        }

        $this->trxMode = isset( $p['trxMode'] ) ? strtoupper( $p['trxMode'] ) : null;
        if ( $this->trxMode &&
            !in_array( $this->trxMode, [ 'DEFERRED', 'IMMEDIATE', 'EXCLUSIVE' ] )
        ) {
            $this->trxMode = null;
            $this->queryLogger->warning( "Invalid SQLite transaction mode provided." );
        }

        $this->lockMgr = new FSLockManager( [
            'domain' => $lockDomain,
            'lockDirectory' => "{$this->dbDir}/locks"
        ] );

        parent::__construct( $p );
    }

    protected static function getAttributes() {
        return [ self::ATTR_DB_LEVEL_LOCKING => true ];
    }

    public static function newStandaloneInstance( $filename, array $p = [] ) {
        $p['dbFilePath'] = $filename;
        $p['schema'] = null;
        $p['tablePrefix'] = '';
        $db = Database::factory( 'sqlite', $p );

        return $db;
    }

    protected function doInitConnection() {
        if ( $this->dbPath !== null ) {
            // Standalone .sqlite file mode.
            $this->openFile(
                $this->dbPath,
                $this->connectionParams['dbname'],
                $this->connectionParams['tablePrefix']
            );
        } elseif ( $this->dbDir !== null ) {
            // Stock wiki mode using standard file names per DB
            if ( strlen( $this->connectionParams['dbname'] ) ) {
                $this->open(
                    $this->connectionParams['host'],
                    $this->connectionParams['user'],
                    $this->connectionParams['password'],
                    $this->connectionParams['dbname'],
                    $this->connectionParams['schema'],
                    $this->connectionParams['tablePrefix']
                );
            } else {
                // Caller will manually call open() later?
                $this->connLogger->debug( __METHOD__ . ': no database opened.' );
            }
        } else {
            throw new InvalidArgumentException( "Need 'dbDirectory' or 'dbFilePath' parameter." );
        }
    }

    function getType() {
        return 'sqlite';
    }

    function implicitGroupby() {
        return false;
    }

    protected function open( $server, $user, $pass, $dbName, $schema, $tablePrefix ) {
        $this->close();
        $fileName = self::generateFileName( $this->dbDir, $dbName );
        if ( !is_readable( $fileName ) ) {
            $this->conn = false;
            throw new DBConnectionError( $this, "SQLite database not accessible" );
        }
        // Only $dbName is used, the other parameters are irrelevant for SQLite databases
        $this->openFile( $fileName, $dbName, $tablePrefix );

        return (bool)$this->conn;
    }

    protected function openFile( $fileName, $dbName, $tablePrefix ) {
        $err = false;

        $this->dbPath = $fileName;
        try {
            if ( $this->flags & self::DBO_PERSISTENT ) {
                $this->conn = new PDO( "sqlite:$fileName", '', '',
                    [ PDO::ATTR_PERSISTENT => true ] );
            } else {
                $this->conn = new PDO( "sqlite:$fileName", '', '' );
            }
        } catch ( PDOException $e ) {
            $err = $e->getMessage();
        }

        if ( !$this->conn ) {
            $this->queryLogger->debug( "DB connection error: $err\n" );
            throw new DBConnectionError( $this, $err );
        }

        $this->opened = is_object( $this->conn );
        if ( $this->opened ) {
            $this->currentDomain = new DatabaseDomain( $dbName, null, $tablePrefix );
            # Set error codes only, don't raise exceptions
            $this->conn->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_SILENT );
            # Enforce LIKE to be case sensitive, just like MySQL
            $this->query( 'PRAGMA case_sensitive_like = 1' );

            $sync = $this->sessionVars['synchronous'] ?? null;
            if ( in_array( $sync, [ 'EXTRA', 'FULL', 'NORMAL' ], true ) ) {
                $this->query( "PRAGMA synchronous = $sync" );
            }

            return $this->conn;
        }

        return false;
    }

    public function getDbFilePath() {
        return $this->dbPath;
    }

    protected function closeConnection() {
        $this->conn = null;

        return true;
    }

    public static function generateFileName( $dir, $dbName ) {
        return "$dir/$dbName.sqlite";
    }

    public function checkForEnabledSearch() {
        if ( self::$fulltextEnabled === null ) {
            self::$fulltextEnabled = false;
            $table = $this->tableName( 'searchindex' );
            $res = $this->query( "SELECT sql FROM sqlite_master WHERE tbl_name = '$table'", __METHOD__ );
            if ( $res ) {
                $row = $res->fetchRow();
                self::$fulltextEnabled = stristr( $row['sql'], 'fts' ) !== false;
            }
        }

        return self::$fulltextEnabled;
    }

    static function getFulltextSearchModule() {
        static $cachedResult = null;
        if ( $cachedResult !== null ) {
            return $cachedResult;
        }
        $cachedResult = false;
        $table = 'dummy_search_test';

        $db = self::newStandaloneInstance( ':memory:' );
        if ( $db->query( "CREATE VIRTUAL TABLE $table USING FTS3(dummy_field)", __METHOD__, true ) ) {
            $cachedResult = 'FTS3';
        }
        $db->close();

        return $cachedResult;
    }

    function attachDatabase( $name, $file = false, $fname = __METHOD__ ) {
        if ( !$file ) {
            $file = self::generateFileName( $this->dbDir, $name );
        }
        $file = $this->addQuotes( $file );

        return $this->query( "ATTACH DATABASE $file AS $name", $fname );
    }

    protected function isWriteQuery( $sql ) {
        return parent::isWriteQuery( $sql ) && !preg_match( '/^(ATTACH|PRAGMA)\b/i', $sql );
    }

    protected function isTransactableQuery( $sql ) {
        return parent::isTransactableQuery( $sql ) && !in_array(
            $this->getQueryVerb( $sql ),
            [ 'ATTACH', 'PRAGMA' ],
            true
        );
    }

    protected function doQuery( $sql ) {
        $res = $this->getBindingHandle()->query( $sql );
        if ( $res === false ) {
            return false;
        }

        $r = $res instanceof ResultWrapper ? $res->result : $res;
        $this->lastAffectedRowCount = $r->rowCount();
        $res = new ResultWrapper( $this, $r->fetchAll() );

        return $res;
    }

    function freeResult( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res->result = null;
        } else {
            $res = null;
        }
    }

    function fetchObject( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $r =& $res->result;
        } else {
            $r =& $res;
        }

        $cur = current( $r );
        if ( is_array( $cur ) ) {
            next( $r );
            $obj = new stdClass;
            foreach ( $cur as $k => $v ) {
                if ( !is_numeric( $k ) ) {
                    $obj->$k = $v;
                }
            }

            return $obj;
        }

        return false;
    }

    function fetchRow( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $r =& $res->result;
        } else {
            $r =& $res;
        }
        $cur = current( $r );
        if ( is_array( $cur ) ) {
            next( $r );

            return $cur;
        }

        return false;
    }

    function numRows( $res ) {
        // false does not implement Countable
        $r = $res instanceof ResultWrapper ? $res->result : $res;

        return is_array( $r ) ? count( $r ) : 0;
    }

    function numFields( $res ) {
        $r = $res instanceof ResultWrapper ? $res->result : $res;
        if ( is_array( $r ) && count( $r ) > 0 ) {
            // The size of the result array is twice the number of fields. (T67578)
            return count( $r[0] ) / 2;
        } else {
            // If the result is empty return 0
            return 0;
        }
    }

    function fieldName( $res, $n ) {
        $r = $res instanceof ResultWrapper ? $res->result : $res;
        if ( is_array( $r ) ) {
            $keys = array_keys( $r[0] );

            return $keys[$n];
        }

        return false;
    }

    function tableName( $name, $format = 'quoted' ) {
        // table names starting with sqlite_ are reserved
        if ( strpos( $name, 'sqlite_' ) === 0 ) {
            return $name;
        }

        return str_replace( '"', '', parent::tableName( $name, $format ) );
    }

    function insertId() {
        // PDO::lastInsertId yields a string :(
        return intval( $this->getBindingHandle()->lastInsertId() );
    }

    function dataSeek( $res, $row ) {
        if ( $res instanceof ResultWrapper ) {
            $r =& $res->result;
        } else {
            $r =& $res;
        }
        reset( $r );
        if ( $row > 0 ) {
            for ( $i = 0; $i < $row; $i++ ) {
                next( $r );
            }
        }
    }

    function lastError() {
        if ( !is_object( $this->conn ) ) {
            return "Cannot return last error, no db connection";
        }
        $e = $this->conn->errorInfo();

        return $e[2] ?? '';
    }

    function lastErrno() {
        if ( !is_object( $this->conn ) ) {
            return "Cannot return last error, no db connection";
        } else {
            $info = $this->conn->errorInfo();

            return $info[1];
        }
    }

    protected function fetchAffectedRowCount() {
        return $this->lastAffectedRowCount;
    }

    function tableExists( $table, $fname = __METHOD__ ) {
        $tableRaw = $this->tableName( $table, 'raw' );
        if ( isset( $this->sessionTempTables[$tableRaw] ) ) {
            return true; // already known to exist
        }

        $encTable = $this->addQuotes( $tableRaw );
        $res = $this->query(
            "SELECT 1 FROM sqlite_master WHERE type='table' AND name=$encTable" );

        return $res->numRows() ? true : false;
    }

    function indexInfo( $table, $index, $fname = __METHOD__ ) {
        $sql = 'PRAGMA index_info(' . $this->addQuotes( $this->indexName( $index ) ) . ')';
        $res = $this->query( $sql, $fname );
        if ( !$res || $res->numRows() == 0 ) {
            return false;
        }
        $info = [];
        foreach ( $res as $row ) {
            $info[] = $row->name;
        }

        return $info;
    }

    function indexUnique( $table, $index, $fname = __METHOD__ ) {
        $row = $this->selectRow( 'sqlite_master', '*',
            [
                'type' => 'index',
                'name' => $this->indexName( $index ),
            ], $fname );
        if ( !$row || !isset( $row->sql ) ) {
            return null;
        }

        // $row->sql will be of the form CREATE [UNIQUE] INDEX ...
        $indexPos = strpos( $row->sql, 'INDEX' );
        if ( $indexPos === false ) {
            return null;
        }
        $firstPart = substr( $row->sql, 0, $indexPos );
        $options = explode( ' ', $firstPart );

        return in_array( 'UNIQUE', $options );
    }

    function makeSelectOptions( $options ) {
        foreach ( $options as $k => $v ) {
            if ( is_numeric( $k ) && ( $v == 'FOR UPDATE' || $v == 'LOCK IN SHARE MODE' ) ) {
                $options[$k] = '';
            }
        }

        return parent::makeSelectOptions( $options );
    }

    protected function makeUpdateOptionsArray( $options ) {
        $options = parent::makeUpdateOptionsArray( $options );
        $options = self::fixIgnore( $options );

        return $options;
    }

    static function fixIgnore( $options ) {
        # SQLite uses OR IGNORE not just IGNORE
        foreach ( $options as $k => $v ) {
            if ( $v == 'IGNORE' ) {
                $options[$k] = 'OR IGNORE';
            }
        }

        return $options;
    }

    function makeInsertOptions( $options ) {
        $options = self::fixIgnore( $options );

        return parent::makeInsertOptions( $options );
    }

    function insert( $table, $a, $fname = __METHOD__, $options = [] ) {
        if ( !count( $a ) ) {
            return true;
        }

        # SQLite can't handle multi-row inserts, so divide up into multiple single-row inserts
        if ( isset( $a[0] ) && is_array( $a[0] ) ) {
            $affectedRowCount = 0;
            try {
                $this->startAtomic( $fname, self::ATOMIC_CANCELABLE );
                foreach ( $a as $v ) {
                    parent::insert( $table, $v, "$fname/multi-row", $options );
                    $affectedRowCount += $this->affectedRows();
                }
                $this->endAtomic( $fname );
            } catch ( Exception $e ) {
                $this->cancelAtomic( $fname );
                throw $e;
            }
            $this->affectedRowCount = $affectedRowCount;
        } else {
            parent::insert( $table, $a, "$fname/single-row", $options );
        }

        return true;
    }

    function replace( $table, $uniqueIndexes, $rows, $fname = __METHOD__ ) {
        if ( !count( $rows ) ) {
            return;
        }

        # SQLite can't handle multi-row replaces, so divide up into multiple single-row queries
        if ( isset( $rows[0] ) && is_array( $rows[0] ) ) {
            $affectedRowCount = 0;
            try {
                $this->startAtomic( $fname, self::ATOMIC_CANCELABLE );
                foreach ( $rows as $v ) {
                    $this->nativeReplace( $table, $v, "$fname/multi-row" );
                    $affectedRowCount += $this->affectedRows();
                }
                $this->endAtomic( $fname );
            } catch ( Exception $e ) {
                $this->cancelAtomic( $fname );
                throw $e;
            }
            $this->affectedRowCount = $affectedRowCount;
        } else {
            $this->nativeReplace( $table, $rows, "$fname/single-row" );
        }
    }

    function textFieldSize( $table, $field ) {
        return -1;
    }

    function unionSupportsOrderAndLimit() {
        return false;
    }

    function unionQueries( $sqls, $all ) {
        $glue = $all ? ' UNION ALL ' : ' UNION ';

        return implode( $glue, $sqls );
    }

    function wasDeadlock() {
        return $this->lastErrno() == 5; // SQLITE_BUSY
    }

    function wasReadOnlyError() {
        return $this->lastErrno() == 8; // SQLITE_READONLY;
    }

    public function wasConnectionError( $errno ) {
        return $errno == 17; // SQLITE_SCHEMA;
    }

    protected function wasKnownStatementRollbackError() {
        // ON CONFLICT ROLLBACK clauses make it so that SQLITE_CONSTRAINT error is
        // ambiguous with regard to whether it implies a ROLLBACK or an ABORT happened.
        // https://sqlite.org/lang_createtable.html#uniqueconst
        // https://sqlite.org/lang_conflict.html
        return false;
    }

    public function getSoftwareLink() {
        return "[{{int:version-db-sqlite-url}} SQLite]";
    }

    function getServerVersion() {
        $ver = $this->getBindingHandle()->getAttribute( PDO::ATTR_SERVER_VERSION );

        return $ver;
    }

    function fieldInfo( $table, $field ) {
        $tableName = $this->tableName( $table );
        $sql = 'PRAGMA table_info(' . $this->addQuotes( $tableName ) . ')';
        $res = $this->query( $sql, __METHOD__ );
        foreach ( $res as $row ) {
            if ( $row->name == $field ) {
                return new SQLiteField( $row, $tableName );
            }
        }

        return false;
    }

    protected function doBegin( $fname = '' ) {
        if ( $this->trxMode ) {
            $this->query( "BEGIN {$this->trxMode}", $fname );
        } else {
            $this->query( 'BEGIN', $fname );
        }
        $this->trxLevel = 1;
    }

    function strencode( $s ) {
        return substr( $this->addQuotes( $s ), 1, -1 );
    }

    function encodeBlob( $b ) {
        return new Blob( $b );
    }

    function decodeBlob( $b ) {
        if ( $b instanceof Blob ) {
            $b = $b->fetch();
        }

        return $b;
    }

    function addQuotes( $s ) {
        if ( $s instanceof Blob ) {
            return "x'" . bin2hex( $s->fetch() ) . "'";
        } elseif ( is_bool( $s ) ) {
            return (int)$s;
        } elseif ( strpos( (string)$s, "\0" ) !== false ) {
            // SQLite doesn't support \0 in strings, so use the hex representation as a workaround.
            // This is a known limitation of SQLite's mprintf function which PDO
            // should work around, but doesn't. I have reported this to php.net as bug #63419:
            // https://bugs.php.net/bug.php?id=63419
            // There was already a similar report for SQLite3::escapeString, bug #62361:
            // https://bugs.php.net/bug.php?id=62361
            // There is an additional bug regarding sorting this data after insert
            // on older versions of sqlite shipped with ubuntu 12.04
            // https://phabricator.wikimedia.org/T74367
            $this->queryLogger->debug(
                __FUNCTION__ .
                ': Quoting value containing null byte. ' .
                'For consistency all binary data should have been ' .
                'first processed with self::encodeBlob()'
            );
            return "x'" . bin2hex( (string)$s ) . "'";
        } else {
            return $this->getBindingHandle()->quote( (string)$s );
        }
    }

    public function buildSubstring( $input, $startPosition, $length = null ) {
        $this->assertBuildSubstringParams( $startPosition, $length );
        $params = [ $input, $startPosition ];
        if ( $length !== null ) {
            $params[] = $length;
        }
        return 'SUBSTR(' . implode( ',', $params ) . ')';
    }

    public function buildStringCast( $field ) {
        return 'CAST ( ' . $field . ' AS TEXT )';
    }

    public function deadlockLoop( /*...*/ ) {
        $args = func_get_args();
        $function = array_shift( $args );

        return $function( ...$args );
    }

    protected function replaceVars( $s ) {
        $s = parent::replaceVars( $s );
        if ( preg_match( '/^\s*(CREATE|ALTER) TABLE/i', $s ) ) {
            // CREATE TABLE hacks to allow schema file sharing with MySQL

            // binary/varbinary column type -> blob
            $s = preg_replace( '/\b(var)?binary(\(\d+\))/i', 'BLOB', $s );
            // no such thing as unsigned
            $s = preg_replace( '/\b(un)?signed\b/i', '', $s );
            // INT -> INTEGER
            $s = preg_replace( '/\b(tiny|small|medium|big|)int(\s*\(\s*\d+\s*\)|\b)/i', 'INTEGER', $s );
            // floating point types -> REAL
            $s = preg_replace(
                '/\b(float|double(\s+precision)?)(\s*\(\s*\d+\s*(,\s*\d+\s*)?\)|\b)/i',
                'REAL',
                $s
            );
            // varchar -> TEXT
            $s = preg_replace( '/\b(var)?char\s*\(.*?\)/i', 'TEXT', $s );
            // TEXT normalization
            $s = preg_replace( '/\b(tiny|medium|long)text\b/i', 'TEXT', $s );
            // BLOB normalization
            $s = preg_replace( '/\b(tiny|small|medium|long|)blob\b/i', 'BLOB', $s );
            // BOOL -> INTEGER
            $s = preg_replace( '/\bbool(ean)?\b/i', 'INTEGER', $s );
            // DATETIME -> TEXT
            $s = preg_replace( '/\b(datetime|timestamp)\b/i', 'TEXT', $s );
            // No ENUM type
            $s = preg_replace( '/\benum\s*\([^)]*\)/i', 'TEXT', $s );
            // binary collation type -> nothing
            $s = preg_replace( '/\bbinary\b/i', '', $s );
            // auto_increment -> autoincrement
            $s = preg_replace( '/\bauto_increment\b/i', 'AUTOINCREMENT', $s );
            // No explicit options
            $s = preg_replace( '/\)[^);]*(;?)\s*$/', ')\1', $s );
            // AUTOINCREMENT should immedidately follow PRIMARY KEY
            $s = preg_replace( '/primary key (.*?) autoincrement/i', 'PRIMARY KEY AUTOINCREMENT $1', $s );
        } elseif ( preg_match( '/^\s*CREATE (\s*(?:UNIQUE|FULLTEXT)\s+)?INDEX/i', $s ) ) {
            // No truncated indexes
            $s = preg_replace( '/\(\d+\)/', '', $s );
            // No FULLTEXT
            $s = preg_replace( '/\bfulltext\b/i', '', $s );
        } elseif ( preg_match( '/^\s*DROP INDEX/i', $s ) ) {
            // DROP INDEX is database-wide, not table-specific, so no ON <table> clause.
            $s = preg_replace( '/\sON\s+[^\s]*/i', '', $s );
        } elseif ( preg_match( '/^\s*INSERT IGNORE\b/i', $s ) ) {
            // INSERT IGNORE --> INSERT OR IGNORE
            $s = preg_replace( '/^\s*INSERT IGNORE\b/i', 'INSERT OR IGNORE', $s );
        }

        return $s;
    }

    public function lock( $lockName, $method, $timeout = 5 ) {
        if ( !is_dir( "{$this->dbDir}/locks" ) ) { // create dir as needed
            if ( !is_writable( $this->dbDir ) || !mkdir( "{$this->dbDir}/locks" ) ) {
                throw new DBError( $this, "Cannot create directory \"{$this->dbDir}/locks\"." );
            }
        }

        return $this->lockMgr->lock( [ $lockName ], LockManager::LOCK_EX, $timeout )->isOK();
    }

    public function unlock( $lockName, $method ) {
        return $this->lockMgr->unlock( [ $lockName ], LockManager::LOCK_EX )->isOK();
    }

    function buildConcat( $stringList ) {
        return '(' . implode( ') || (', $stringList ) . ')';
    }

    public function buildGroupConcatField(
        $delim, $table, $field, $conds = '', $join_conds = []
    ) {
        $fld = "group_concat($field," . $this->addQuotes( $delim ) . ')';

        return '(' . $this->selectSQLText( $table, $fld, $conds, null, [], $join_conds ) . ')';
    }

    function duplicateTableStructure( $oldName, $newName, $temporary = false, $fname = __METHOD__ ) {
        $res = $this->query( "SELECT sql FROM sqlite_master WHERE tbl_name=" .
            $this->addQuotes( $oldName ) . " AND type='table'", $fname );
        $obj = $this->fetchObject( $res );
        if ( !$obj ) {
            throw new RuntimeException( "Couldn't retrieve structure for table $oldName" );
        }
        $sql = $obj->sql;
        $sql = preg_replace(
            '/(?<=\W)"?' .
                preg_quote( trim( $this->addIdentifierQuotes( $oldName ), '"' ), '/' ) .
                '"?(?=\W)/',
            $this->addIdentifierQuotes( $newName ),
            $sql,
            1
        );
        if ( $temporary ) {
            if ( preg_match( '/^\\s*CREATE\\s+VIRTUAL\\s+TABLE\b/i', $sql ) ) {
                $this->queryLogger->debug(
                    "Table $oldName is virtual, can't create a temporary duplicate.\n" );
            } else {
                $sql = str_replace( 'CREATE TABLE', 'CREATE TEMPORARY TABLE', $sql );
            }
        }

        $res = $this->query( $sql, $fname, self::QUERY_PSEUDO_PERMANENT );

        // Take over indexes
        $indexList = $this->query( 'PRAGMA INDEX_LIST(' . $this->addQuotes( $oldName ) . ')' );
        foreach ( $indexList as $index ) {
            if ( strpos( $index->name, 'sqlite_autoindex' ) === 0 ) {
                continue;
            }

            if ( $index->unique ) {
                $sql = 'CREATE UNIQUE INDEX';
            } else {
                $sql = 'CREATE INDEX';
            }
            // Try to come up with a new index name, given indexes have database scope in SQLite
            $indexName = $newName . '_' . $index->name;
            $sql .= ' ' . $indexName . ' ON ' . $newName;

            $indexInfo = $this->query( 'PRAGMA INDEX_INFO(' . $this->addQuotes( $index->name ) . ')' );
            $fields = [];
            foreach ( $indexInfo as $indexInfoRow ) {
                $fields[$indexInfoRow->seqno] = $indexInfoRow->name;
            }

            $sql .= '(' . implode( ',', $fields ) . ')';

            $this->query( $sql );
        }

        return $res;
    }

    function listTables( $prefix = null, $fname = __METHOD__ ) {
        $result = $this->select(
            'sqlite_master',
            'name',
            "type='table'"
        );

        $endArray = [];

        foreach ( $result as $table ) {
            $vars = get_object_vars( $table );
            $table = array_pop( $vars );

            if ( !$prefix || strpos( $table, $prefix ) === 0 ) {
                if ( strpos( $table, 'sqlite_' ) !== 0 ) {
                    $endArray[] = $table;
                }
            }
        }

        return $endArray;
    }

    public function dropTable( $tableName, $fName = __METHOD__ ) {
        if ( !$this->tableExists( $tableName, $fName ) ) {
            return false;
        }
        $sql = "DROP TABLE " . $this->tableName( $tableName );

        return $this->query( $sql, $fName );
    }

    public function setTableAliases( array $aliases ) {
        parent::setTableAliases( $aliases );
        foreach ( $this->tableAliases as $params ) {
            if ( isset( $this->alreadyAttached[$params['dbname']] ) ) {
                continue;
            }
            $this->attachDatabase( $params['dbname'] );
            $this->alreadyAttached[$params['dbname']] = true;
        }
    }

    public function resetSequenceForTable( $table, $fname = __METHOD__ ) {
        $encTable = $this->addIdentifierQuotes( 'sqlite_sequence' );
        $encName = $this->addQuotes( $this->tableName( $table, 'raw' ) );
        $this->query( "DELETE FROM $encTable WHERE name = $encName", $fname );
    }

    public function databasesAreIndependent() {
        return true;
    }

    public function __toString() {
        return is_object( $this->conn )
            ? 'SQLite ' . (string)$this->conn->getAttribute( PDO::ATTR_SERVER_VERSION )
            : '(not connected)';
    }

    protected function getBindingHandle() {
        return parent::getBindingHandle();
    }
}

class_alias( DatabaseSqlite::class, 'DatabaseSqlite' );