4 * @defgroup Database Database
6 * This file deals with database interface functions
7 * and query specifics/optimisations.
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License as published by
11 * the Free Software Foundation; either version 2 of the License, or
12 * (at your option) any later version.
14 * This program is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 * GNU General Public License for more details.
19 * You should have received a copy of the GNU General Public License along
20 * with this program; if not, write to the Free Software Foundation, Inc.,
21 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
22 * http://www.gnu.org/copyleft/gpl.html
29 * Basic database interface for live and lazy-loaded DB handles
31 * @note: IDatabase and DBConnRef should be updated to reflect any changes
35 /** @var int Callback triggered immediately due to no active transaction */
36 const TRIGGER_IDLE
= 1;
37 /** @var int Callback triggered by COMMIT */
38 const TRIGGER_COMMIT
= 2;
39 /** @var int Callback triggered by ROLLBACK */
40 const TRIGGER_ROLLBACK
= 3;
42 /** @var string Transaction is requested by regular caller outside of the DB layer */
43 const TRANSACTION_EXPLICIT
= '';
44 /** @var string Transaction is requested internally via DBO_TRX/startAtomic() */
45 const TRANSACTION_INTERNAL
= 'implicit';
47 /** @var string Transaction operation comes from service managing all DBs */
48 const FLUSHING_ALL_PEERS
= 'flush';
49 /** @var string Transaction operation comes from the database class internally */
50 const FLUSHING_INTERNAL
= 'flush';
52 /** @var string Do not remember the prior flags */
53 const REMEMBER_NOTHING
= '';
54 /** @var string Remember the prior flags */
55 const REMEMBER_PRIOR
= 'remember';
56 /** @var string Restore to the prior flag state */
57 const RESTORE_PRIOR
= 'prior';
58 /** @var string Restore to the initial flag state */
59 const RESTORE_INITIAL
= 'initial';
61 /** @var string Estimate total time (RTT, scanning, waiting on locks, applying) */
62 const ESTIMATE_TOTAL
= 'total';
63 /** @var string Estimate time to apply (scanning, applying) */
64 const ESTIMATE_DB_APPLY
= 'apply';
67 * A string describing the current software version, and possibly
68 * other details in a user-friendly way. Will be listed on Special:Version, etc.
69 * Use getServerVersion() to get machine-friendly information.
71 * @return string Version information from the database server
73 public function getServerInfo();
76 * Turns buffering of SQL result sets on (true) or off (false). Default is
79 * Unbuffered queries are very troublesome in MySQL:
81 * - If another query is executed while the first query is being read
82 * out, the first query is killed. This means you can't call normal
83 * MediaWiki functions while you are reading an unbuffered query result
84 * from a normal wfGetDB() connection.
86 * - Unbuffered queries cause the MySQL server to use large amounts of
87 * memory and to hold broad locks which block other queries.
89 * If you want to limit client-side memory, it's almost always better to
90 * split up queries into batches using a LIMIT clause than to switch off
93 * @param null|bool $buffer
94 * @return null|bool The previous value of the flag
96 public function bufferResults( $buffer = null );
99 * Gets the current transaction level.
101 * Historically, transactions were allowed to be "nested". This is no
102 * longer supported, so this function really only returns a boolean.
104 * @return int The previous value
106 public function trxLevel();
109 * Get the UNIX timestamp of the time that the transaction was established
111 * This can be used to reason about the staleness of SELECT data
112 * in REPEATABLE-READ transaction isolation level.
114 * @return float|null Returns null if there is not active transaction
117 public function trxTimestamp();
120 * @return bool Whether an explicit transaction or atomic sections are still open
123 public function explicitTrxActive();
126 * Get/set the table prefix.
127 * @param string $prefix The table prefix to set, or omitted to leave it unchanged.
128 * @return string The previous table prefix.
130 public function tablePrefix( $prefix = null );
133 * Get/set the db schema.
134 * @param string $schema The database schema to set, or omitted to leave it unchanged.
135 * @return string The previous db schema.
137 public function dbSchema( $schema = null );
140 * Get properties passed down from the server info array of the load
143 * @param string $name The entry of the info array to get, or null to get the
146 * @return array|mixed|null
148 public function getLBInfo( $name = null );
151 * Set the LB info array, or a member of it. If called with one parameter,
152 * the LB info array is set to that parameter. If it is called with two
153 * parameters, the member with the given name is set to the given value.
155 * @param string $name
156 * @param array $value
158 public function setLBInfo( $name, $value = null );
161 * Returns true if this database does an implicit sort when doing GROUP BY
165 public function implicitGroupby();
168 * Returns true if this database does an implicit order by when the column has an index
169 * For example: SELECT page_title FROM page LIMIT 1
173 public function implicitOrderby();
176 * Return the last query that went through IDatabase::query()
179 public function lastQuery();
182 * Returns true if the connection may have been used for write queries.
183 * Should return true if unsure.
187 public function doneWrites();
190 * Returns the last time the connection may have been used for write queries.
191 * Should return a timestamp if unsure.
193 * @return int|float UNIX timestamp or false
196 public function lastDoneWrites();
199 * @return bool Whether there is a transaction open with possible write queries
202 public function writesPending();
205 * Returns true if there is a transaction open with possible write
206 * queries or transaction pre-commit/idle callbacks waiting on it to finish.
207 * This does *not* count recurring callbacks, e.g. from setTransactionListener().
211 public function writesOrCallbacksPending();
214 * Get the time spend running write queries for this transaction
216 * High times could be due to scanning, updates, locking, and such
218 * @param string $type IDatabase::ESTIMATE_* constant [default: ESTIMATE_ALL]
219 * @return float|bool Returns false if not transaction is active
222 public function pendingWriteQueryDuration( $type = self
::ESTIMATE_TOTAL
);
225 * Get the list of method names that did write queries for this transaction
230 public function pendingWriteCallers();
233 * Is a connection to the database open?
236 public function isOpen();
239 * Set a flag for this connection
241 * @param int $flag DBO_* constants from Defines.php:
242 * - DBO_DEBUG: output some debug info (same as debug())
243 * - DBO_NOBUFFER: don't buffer results (inverse of bufferResults())
244 * - DBO_TRX: automatically start transactions
245 * - DBO_DEFAULT: automatically sets DBO_TRX if not in command line mode
246 * and removes it in command line mode
247 * - DBO_PERSISTENT: use persistant database connection
248 * @param string $remember IDatabase::REMEMBER_* constant [default: REMEMBER_NOTHING]
250 public function setFlag( $flag, $remember = self
::REMEMBER_NOTHING
);
253 * Clear a flag for this connection
255 * @param int $flag DBO_* constants from Defines.php:
256 * - DBO_DEBUG: output some debug info (same as debug())
257 * - DBO_NOBUFFER: don't buffer results (inverse of bufferResults())
258 * - DBO_TRX: automatically start transactions
259 * - DBO_DEFAULT: automatically sets DBO_TRX if not in command line mode
260 * and removes it in command line mode
261 * - DBO_PERSISTENT: use persistant database connection
262 * @param string $remember IDatabase::REMEMBER_* constant [default: REMEMBER_NOTHING]
264 public function clearFlag( $flag, $remember = self
::REMEMBER_NOTHING
);
267 * Restore the flags to their prior state before the last setFlag/clearFlag call
269 * @param string $state IDatabase::RESTORE_* constant. [default: RESTORE_PRIOR]
272 public function restoreFlags( $state = self
::RESTORE_PRIOR
);
275 * Returns a boolean whether the flag $flag is set for this connection
277 * @param int $flag DBO_* constants from Defines.php:
278 * - DBO_DEBUG: output some debug info (same as debug())
279 * - DBO_NOBUFFER: don't buffer results (inverse of bufferResults())
280 * - DBO_TRX: automatically start transactions
281 * - DBO_PERSISTENT: use persistant database connection
284 public function getFlag( $flag );
287 * General read-only accessor
289 * @param string $name
292 public function getProperty( $name );
297 public function getWikiID();
300 * Get the type of the DBMS, as it appears in $wgDBtype.
304 public function getType();
307 * Open a connection to the database. Usually aborts on failure
309 * @param string $server Database server host
310 * @param string $user Database user name
311 * @param string $password Database user password
312 * @param string $dbName Database name
314 * @throws DBConnectionError
316 public function open( $server, $user, $password, $dbName );
319 * Fetch the next row from the given result object, in object form.
320 * Fields can be retrieved with $row->fieldname, with fields acting like
322 * If no more rows are available, false is returned.
324 * @param ResultWrapper|stdClass $res Object as returned from IDatabase::query(), etc.
325 * @return stdClass|bool
326 * @throws DBUnexpectedError Thrown if the database returns an error
328 public function fetchObject( $res );
331 * Fetch the next row from the given result object, in associative array
332 * form. Fields are retrieved with $row['fieldname'].
333 * If no more rows are available, false is returned.
335 * @param ResultWrapper $res Result object as returned from IDatabase::query(), etc.
337 * @throws DBUnexpectedError Thrown if the database returns an error
339 public function fetchRow( $res );
342 * Get the number of rows in a result object
344 * @param mixed $res A SQL result
347 public function numRows( $res );
350 * Get the number of fields in a result object
351 * @see http://www.php.net/mysql_num_fields
353 * @param mixed $res A SQL result
356 public function numFields( $res );
359 * Get a field name in a result object
360 * @see http://www.php.net/mysql_field_name
362 * @param mixed $res A SQL result
366 public function fieldName( $res, $n );
369 * Get the inserted value of an auto-increment row
371 * The value inserted should be fetched from nextSequenceValue()
374 * $id = $dbw->nextSequenceValue( 'page_page_id_seq' );
375 * $dbw->insert( 'page', [ 'page_id' => $id ] );
376 * $id = $dbw->insertId();
380 public function insertId();
383 * Change the position of the cursor in a result object
384 * @see http://www.php.net/mysql_data_seek
386 * @param mixed $res A SQL result
389 public function dataSeek( $res, $row );
392 * Get the last error number
393 * @see http://www.php.net/mysql_errno
397 public function lastErrno();
400 * Get a description of the last error
401 * @see http://www.php.net/mysql_error
405 public function lastError();
408 * mysql_fetch_field() wrapper
409 * Returns false if the field doesn't exist
411 * @param string $table Table name
412 * @param string $field Field name
416 public function fieldInfo( $table, $field );
419 * Get the number of rows affected by the last write query
420 * @see http://www.php.net/mysql_affected_rows
424 public function affectedRows();
427 * Returns a wikitext link to the DB's website, e.g.,
428 * return "[http://www.mysql.com/ MySQL]";
429 * Should at least contain plain text, if for some reason
430 * your database has no website.
432 * @return string Wikitext of a link to the server software's web site
434 public function getSoftwareLink();
437 * A string describing the current software version, like from
438 * mysql_get_server_info().
440 * @return string Version information from the database server.
442 public function getServerVersion();
445 * Closes a database connection.
446 * if it is open : commits any open transactions
449 * @return bool Operation success. true if already closed.
451 public function close();
454 * @param string $error Fallback error message, used if none is given by DB
455 * @throws DBConnectionError
457 public function reportConnectionError( $error = 'Unknown error' );
460 * Run an SQL query and return the result. Normally throws a DBQueryError
461 * on failure. If errors are ignored, returns false instead.
463 * In new code, the query wrappers select(), insert(), update(), delete(),
464 * etc. should be used where possible, since they give much better DBMS
465 * independence and automatically quote or validate user input in a variety
466 * of contexts. This function is generally only useful for queries which are
467 * explicitly DBMS-dependent and are unsupported by the query wrappers, such
470 * However, the query wrappers themselves should call this function.
472 * @param string $sql SQL query
473 * @param string $fname Name of the calling function, for profiling/SHOW PROCESSLIST
474 * comment (you can use __METHOD__ or add some extra info)
475 * @param bool $tempIgnore Whether to avoid throwing an exception on errors...
476 * maybe best to catch the exception instead?
478 * @return bool|ResultWrapper True for a successful write query, ResultWrapper object
479 * for a successful read query, or false on failure if $tempIgnore set
481 public function query( $sql, $fname = __METHOD__
, $tempIgnore = false );
484 * Report a query error. Log the error, and if neither the object ignore
485 * flag nor the $tempIgnore flag is set, throw a DBQueryError.
487 * @param string $error
490 * @param string $fname
491 * @param bool $tempIgnore
492 * @throws DBQueryError
494 public function reportQueryError( $error, $errno, $sql, $fname, $tempIgnore = false );
497 * Free a result object returned by query() or select(). It's usually not
498 * necessary to call this, just use unset() or let the variable holding
499 * the result object go out of scope.
501 * @param mixed $res A SQL result
503 public function freeResult( $res );
506 * A SELECT wrapper which returns a single field from a single result row.
508 * Usually throws a DBQueryError on failure. If errors are explicitly
509 * ignored, returns false on failure.
511 * If no result rows are returned from the query, false is returned.
513 * @param string|array $table Table name. See IDatabase::select() for details.
514 * @param string $var The field name to select. This must be a valid SQL
515 * fragment: do not use unvalidated user input.
516 * @param string|array $cond The condition array. See IDatabase::select() for details.
517 * @param string $fname The function name of the caller.
518 * @param string|array $options The query options. See IDatabase::select() for details.
520 * @return bool|mixed The value from the field, or false on failure.
522 public function selectField(
523 $table, $var, $cond = '', $fname = __METHOD__
, $options = []
527 * A SELECT wrapper which returns a list of single field values from result rows.
529 * Usually throws a DBQueryError on failure. If errors are explicitly
530 * ignored, returns false on failure.
532 * If no result rows are returned from the query, false is returned.
534 * @param string|array $table Table name. See IDatabase::select() for details.
535 * @param string $var The field name to select. This must be a valid SQL
536 * fragment: do not use unvalidated user input.
537 * @param string|array $cond The condition array. See IDatabase::select() for details.
538 * @param string $fname The function name of the caller.
539 * @param string|array $options The query options. See IDatabase::select() for details.
541 * @return bool|array The values from the field, or false on failure
544 public function selectFieldValues(
545 $table, $var, $cond = '', $fname = __METHOD__
, $options = []
549 * Execute a SELECT query constructed using the various parameters provided.
550 * See below for full details of the parameters.
552 * @param string|array $table Table name
553 * @param string|array $vars Field names
554 * @param string|array $conds Conditions
555 * @param string $fname Caller function name
556 * @param array $options Query options
557 * @param array $join_conds Join conditions
560 * @param string|array $table
562 * May be either an array of table names, or a single string holding a table
563 * name. If an array is given, table aliases can be specified, for example:
567 * This includes the user table in the query, with the alias "a" available
568 * for use in field names (e.g. a.user_name).
570 * All of the table names given here are automatically run through
571 * DatabaseBase::tableName(), which causes the table prefix (if any) to be
572 * added, and various other table name mappings to be performed.
574 * Do not use untrusted user input as a table name. Alias names should
575 * not have characters outside of the Basic multilingual plane.
577 * @param string|array $vars
579 * May be either a field name or an array of field names. The field names
580 * can be complete fragments of SQL, for direct inclusion into the SELECT
581 * query. If an array is given, field aliases can be specified, for example:
583 * [ 'maxrev' => 'MAX(rev_id)' ]
585 * This includes an expression with the alias "maxrev" in the query.
587 * If an expression is given, care must be taken to ensure that it is
590 * Untrusted user input must not be passed to this parameter.
592 * @param string|array $conds
594 * May be either a string containing a single condition, or an array of
595 * conditions. If an array is given, the conditions constructed from each
596 * element are combined with AND.
598 * Array elements may take one of two forms:
600 * - Elements with a numeric key are interpreted as raw SQL fragments.
601 * - Elements with a string key are interpreted as equality conditions,
602 * where the key is the field name.
603 * - If the value of such an array element is a scalar (such as a
604 * string), it will be treated as data and thus quoted appropriately.
605 * If it is null, an IS NULL clause will be added.
606 * - If the value is an array, an IN (...) clause will be constructed
607 * from its non-null elements, and an IS NULL clause will be added
608 * if null is present, such that the field may match any of the
609 * elements in the array. The non-null elements will be quoted.
611 * Note that expressions are often DBMS-dependent in their syntax.
612 * DBMS-independent wrappers are provided for constructing several types of
613 * expression commonly used in condition queries. See:
614 * - IDatabase::buildLike()
615 * - IDatabase::conditional()
617 * Untrusted user input is safe in the values of string keys, however untrusted
618 * input must not be used in the array key names or in the values of numeric keys.
619 * Escaping of untrusted input used in values of numeric keys should be done via
620 * IDatabase::addQuotes()
622 * @param string|array $options
624 * Optional: Array of query options. Boolean options are specified by
625 * including them in the array as a string value with a numeric key, for
630 * The supported options are:
632 * - OFFSET: Skip this many rows at the start of the result set. OFFSET
633 * with LIMIT can theoretically be used for paging through a result set,
634 * but this is discouraged in MediaWiki for performance reasons.
636 * - LIMIT: Integer: return at most this many rows. The rows are sorted
637 * and then the first rows are taken until the limit is reached. LIMIT
638 * is applied to a result set after OFFSET.
640 * - FOR UPDATE: Boolean: lock the returned rows so that they can't be
641 * changed until the next COMMIT.
643 * - DISTINCT: Boolean: return only unique result rows.
645 * - GROUP BY: May be either an SQL fragment string naming a field or
646 * expression to group by, or an array of such SQL fragments.
648 * - HAVING: May be either an string containing a HAVING clause or an array of
649 * conditions building the HAVING clause. If an array is given, the conditions
650 * constructed from each element are combined with AND.
652 * - ORDER BY: May be either an SQL fragment giving a field name or
653 * expression to order by, or an array of such SQL fragments.
655 * - USE INDEX: This may be either a string giving the index name to use
656 * for the query, or an array. If it is an associative array, each key
657 * gives the table name (or alias), each value gives the index name to
658 * use for that table. All strings are SQL fragments and so should be
659 * validated by the caller.
661 * - EXPLAIN: In MySQL, this causes an EXPLAIN SELECT query to be run,
664 * And also the following boolean MySQL extensions, see the MySQL manual
667 * - LOCK IN SHARE MODE
671 * - SQL_BUFFER_RESULT
673 * - SQL_CALC_FOUND_ROWS
678 * @param string|array $join_conds
680 * Optional associative array of table-specific join conditions. In the
681 * most common case, this is unnecessary, since the join condition can be
682 * in $conds. However, it is useful for doing a LEFT JOIN.
684 * The key of the array contains the table name or alias. The value is an
685 * array with two elements, numbered 0 and 1. The first gives the type of
686 * join, the second is the same as the $conds parameter. Thus it can be
687 * an SQL fragment, or an array where the string keys are equality and the
688 * numeric keys are SQL fragments all AND'd together. For example:
690 * [ 'page' => [ 'LEFT JOIN', 'page_latest=rev_id' ] ]
692 * @return ResultWrapper|bool If the query returned no rows, a ResultWrapper
693 * with no rows in it will be returned. If there was a query error, a
694 * DBQueryError exception will be thrown, except if the "ignore errors"
695 * option was set, in which case false will be returned.
697 public function select(
698 $table, $vars, $conds = '', $fname = __METHOD__
,
699 $options = [], $join_conds = []
703 * The equivalent of IDatabase::select() except that the constructed SQL
704 * is returned, instead of being immediately executed. This can be useful for
705 * doing UNION queries, where the SQL text of each query is needed. In general,
706 * however, callers outside of Database classes should just use select().
708 * @param string|array $table Table name
709 * @param string|array $vars Field names
710 * @param string|array $conds Conditions
711 * @param string $fname Caller function name
712 * @param string|array $options Query options
713 * @param string|array $join_conds Join conditions
715 * @return string SQL query string.
716 * @see IDatabase::select()
718 public function selectSQLText(
719 $table, $vars, $conds = '', $fname = __METHOD__
,
720 $options = [], $join_conds = []
724 * Single row SELECT wrapper. Equivalent to IDatabase::select(), except
725 * that a single row object is returned. If the query returns no rows,
728 * @param string|array $table Table name
729 * @param string|array $vars Field names
730 * @param array $conds Conditions
731 * @param string $fname Caller function name
732 * @param string|array $options Query options
733 * @param array|string $join_conds Join conditions
735 * @return stdClass|bool
737 public function selectRow( $table, $vars, $conds, $fname = __METHOD__
,
738 $options = [], $join_conds = []
742 * Estimate the number of rows in dataset
744 * MySQL allows you to estimate the number of rows that would be returned
745 * by a SELECT query, using EXPLAIN SELECT. The estimate is provided using
746 * index cardinality statistics, and is notoriously inaccurate, especially
747 * when large numbers of rows have recently been added or deleted.
749 * For DBMSs that don't support fast result size estimation, this function
750 * will actually perform the SELECT COUNT(*).
752 * Takes the same arguments as IDatabase::select().
754 * @param string $table Table name
755 * @param string $vars Unused
756 * @param array|string $conds Filters on the table
757 * @param string $fname Function name for profiling
758 * @param array $options Options for select
759 * @return int Row count
761 public function estimateRowCount(
762 $table, $vars = '*', $conds = '', $fname = __METHOD__
, $options = []
766 * Get the number of rows in dataset
768 * This is useful when trying to do COUNT(*) but with a LIMIT for performance.
770 * Takes the same arguments as IDatabase::select().
772 * @since 1.27 Added $join_conds parameter
774 * @param array|string $tables Table names
775 * @param string $vars Unused
776 * @param array|string $conds Filters on the table
777 * @param string $fname Function name for profiling
778 * @param array $options Options for select
779 * @param array $join_conds Join conditions (since 1.27)
780 * @return int Row count
782 public function selectRowCount(
783 $tables, $vars = '*', $conds = '', $fname = __METHOD__
, $options = [], $join_conds = []
787 * Determines whether a field exists in a table
789 * @param string $table Table name
790 * @param string $field Filed to check on that table
791 * @param string $fname Calling function name (optional)
792 * @return bool Whether $table has filed $field
794 public function fieldExists( $table, $field, $fname = __METHOD__
);
797 * Determines whether an index exists
798 * Usually throws a DBQueryError on failure
799 * If errors are explicitly ignored, returns NULL on failure
801 * @param string $table
802 * @param string $index
803 * @param string $fname
806 public function indexExists( $table, $index, $fname = __METHOD__
);
809 * Query whether a given table exists
811 * @param string $table
812 * @param string $fname
815 public function tableExists( $table, $fname = __METHOD__
);
818 * Determines if a given index is unique
820 * @param string $table
821 * @param string $index
825 public function indexUnique( $table, $index );
828 * INSERT wrapper, inserts an array into a table.
832 * - A single associative array. The array keys are the field names, and
833 * the values are the values to insert. The values are treated as data
834 * and will be quoted appropriately. If NULL is inserted, this will be
835 * converted to a database NULL.
836 * - An array with numeric keys, holding a list of associative arrays.
837 * This causes a multi-row INSERT on DBMSs that support it. The keys in
838 * each subarray must be identical to each other, and in the same order.
840 * Usually throws a DBQueryError on failure. If errors are explicitly ignored,
843 * $options is an array of options, with boolean options encoded as values
844 * with numeric keys, in the same style as $options in
845 * IDatabase::select(). Supported options are:
847 * - IGNORE: Boolean: if present, duplicate key errors are ignored, and
848 * any rows which cause duplicate key errors are not inserted. It's
849 * possible to determine how many rows were successfully inserted using
850 * IDatabase::affectedRows().
852 * @param string $table Table name. This will be passed through
853 * DatabaseBase::tableName().
854 * @param array $a Array of rows to insert
855 * @param string $fname Calling function name (use __METHOD__) for logs/profiling
856 * @param array $options Array of options
860 public function insert( $table, $a, $fname = __METHOD__
, $options = [] );
863 * UPDATE wrapper. Takes a condition array and a SET array.
865 * @param string $table Name of the table to UPDATE. This will be passed through
866 * DatabaseBase::tableName().
867 * @param array $values An array of values to SET. For each array element,
868 * the key gives the field name, and the value gives the data to set
869 * that field to. The data will be quoted by IDatabase::addQuotes().
870 * @param array $conds An array of conditions (WHERE). See
871 * IDatabase::select() for the details of the format of condition
872 * arrays. Use '*' to update all rows.
873 * @param string $fname The function name of the caller (from __METHOD__),
874 * for logging and profiling.
875 * @param array $options An array of UPDATE options, can be:
876 * - IGNORE: Ignore unique key conflicts
877 * - LOW_PRIORITY: MySQL-specific, see MySQL manual.
880 public function update( $table, $values, $conds, $fname = __METHOD__
, $options = [] );
883 * Makes an encoded list of strings from an array
885 * @param array $a Containing the data
886 * @param int $mode Constant
887 * - LIST_COMMA: Comma separated, no field names
888 * - LIST_AND: ANDed WHERE clause (without the WHERE). See the
889 * documentation for $conds in IDatabase::select().
890 * - LIST_OR: ORed WHERE clause (without the WHERE)
891 * - LIST_SET: Comma separated with field names, like a SET clause
892 * - LIST_NAMES: Comma separated field names
896 public function makeList( $a, $mode = LIST_COMMA
);
899 * Build a partial where clause from a 2-d array such as used for LinkBatch.
900 * The keys on each level may be either integers or strings.
902 * @param array $data Organized as 2-d
903 * [ baseKeyVal => [ subKeyVal => [ignored], ... ], ... ]
904 * @param string $baseKey Field name to match the base-level keys to (eg 'pl_namespace')
905 * @param string $subKey Field name to match the sub-level keys to (eg 'pl_title')
906 * @return string|bool SQL fragment, or false if no items in array
908 public function makeWhereFrom2d( $data, $baseKey, $subKey );
911 * @param string $field
914 public function bitNot( $field );
917 * @param string $fieldLeft
918 * @param string $fieldRight
921 public function bitAnd( $fieldLeft, $fieldRight );
924 * @param string $fieldLeft
925 * @param string $fieldRight
928 public function bitOr( $fieldLeft, $fieldRight );
931 * Build a concatenation list to feed into a SQL query
932 * @param array $stringList List of raw SQL expressions; caller is
933 * responsible for any quoting
936 public function buildConcat( $stringList );
939 * Build a GROUP_CONCAT or equivalent statement for a query.
941 * This is useful for combining a field for several rows into a single string.
942 * NULL values will not appear in the output, duplicated values will appear,
943 * and the resulting delimiter-separated values have no defined sort order.
944 * Code using the results may need to use the PHP unique() or sort() methods.
946 * @param string $delim Glue to bind the results together
947 * @param string|array $table Table name
948 * @param string $field Field name
949 * @param string|array $conds Conditions
950 * @param string|array $join_conds Join conditions
951 * @return string SQL text
954 public function buildGroupConcatField(
955 $delim, $table, $field, $conds = '', $join_conds = []
959 * Change the current database
962 * @return bool Success or failure
964 public function selectDB( $db );
967 * Get the current DB name
970 public function getDBname();
973 * Get the server hostname or IP address
976 public function getServer();
979 * Adds quotes and backslashes.
981 * @param string|Blob $s
984 public function addQuotes( $s );
987 * LIKE statement wrapper, receives a variable-length argument list with
988 * parts of pattern to match containing either string literals that will be
989 * escaped or tokens returned by anyChar() or anyString(). Alternatively,
990 * the function could be provided with an array of aforementioned
993 * Example: $dbr->buildLike( 'My_page_title/', $dbr->anyString() ) returns
994 * a LIKE clause that searches for subpages of 'My page title'.
996 * $pattern = [ 'My_page_title/', $dbr->anyString() ];
997 * $query .= $dbr->buildLike( $pattern );
1000 * @return string Fully built LIKE statement
1002 public function buildLike();
1005 * Returns a token for buildLike() that denotes a '_' to be used in a LIKE query
1009 public function anyChar();
1012 * Returns a token for buildLike() that denotes a '%' to be used in a LIKE query
1016 public function anyString();
1019 * Returns an appropriately quoted sequence value for inserting a new row.
1020 * MySQL has autoincrement fields, so this is just NULL. But the PostgreSQL
1021 * subclass will return an integer, and save the value for insertId()
1023 * Any implementation of this function should *not* involve reusing
1024 * sequence numbers created for rolled-back transactions.
1025 * See http://bugs.mysql.com/bug.php?id=30767 for details.
1026 * @param string $seqName
1029 public function nextSequenceValue( $seqName );
1032 * REPLACE query wrapper.
1034 * REPLACE is a very handy MySQL extension, which functions like an INSERT
1035 * except that when there is a duplicate key error, the old row is deleted
1036 * and the new row is inserted in its place.
1038 * We simulate this with standard SQL with a DELETE followed by INSERT. To
1039 * perform the delete, we need to know what the unique indexes are so that
1040 * we know how to find the conflicting rows.
1042 * It may be more efficient to leave off unique indexes which are unlikely
1043 * to collide. However if you do this, you run the risk of encountering
1044 * errors which wouldn't have occurred in MySQL.
1046 * @param string $table The table to replace the row(s) in.
1047 * @param array $uniqueIndexes Is an array of indexes. Each element may be either
1048 * a field name or an array of field names
1049 * @param array $rows Can be either a single row to insert, or multiple rows,
1050 * in the same format as for IDatabase::insert()
1051 * @param string $fname Calling function name (use __METHOD__) for logs/profiling
1053 public function replace( $table, $uniqueIndexes, $rows, $fname = __METHOD__
);
1056 * INSERT ON DUPLICATE KEY UPDATE wrapper, upserts an array into a table.
1058 * This updates any conflicting rows (according to the unique indexes) using
1059 * the provided SET clause and inserts any remaining (non-conflicted) rows.
1061 * $rows may be either:
1062 * - A single associative array. The array keys are the field names, and
1063 * the values are the values to insert. The values are treated as data
1064 * and will be quoted appropriately. If NULL is inserted, this will be
1065 * converted to a database NULL.
1066 * - An array with numeric keys, holding a list of associative arrays.
1067 * This causes a multi-row INSERT on DBMSs that support it. The keys in
1068 * each subarray must be identical to each other, and in the same order.
1070 * It may be more efficient to leave off unique indexes which are unlikely
1071 * to collide. However if you do this, you run the risk of encountering
1072 * errors which wouldn't have occurred in MySQL.
1074 * Usually throws a DBQueryError on failure. If errors are explicitly ignored,
1079 * @param string $table Table name. This will be passed through DatabaseBase::tableName().
1080 * @param array $rows A single row or list of rows to insert
1081 * @param array $uniqueIndexes List of single field names or field name tuples
1082 * @param array $set An array of values to SET. For each array element, the
1083 * key gives the field name, and the value gives the data to set that
1084 * field to. The data will be quoted by IDatabase::addQuotes().
1085 * @param string $fname Calling function name (use __METHOD__) for logs/profiling
1089 public function upsert(
1090 $table, array $rows, array $uniqueIndexes, array $set, $fname = __METHOD__
1094 * DELETE where the condition is a join.
1096 * MySQL overrides this to use a multi-table DELETE syntax, in other databases
1097 * we use sub-selects
1099 * For safety, an empty $conds will not delete everything. If you want to
1100 * delete all rows where the join condition matches, set $conds='*'.
1102 * DO NOT put the join condition in $conds.
1104 * @param string $delTable The table to delete from.
1105 * @param string $joinTable The other table.
1106 * @param string $delVar The variable to join on, in the first table.
1107 * @param string $joinVar The variable to join on, in the second table.
1108 * @param array $conds Condition array of field names mapped to variables,
1109 * ANDed together in the WHERE clause
1110 * @param string $fname Calling function name (use __METHOD__) for logs/profiling
1111 * @throws DBUnexpectedError
1113 public function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds,
1118 * DELETE query wrapper.
1120 * @param array $table Table name
1121 * @param string|array $conds Array of conditions. See $conds in IDatabase::select()
1122 * for the format. Use $conds == "*" to delete all rows
1123 * @param string $fname Name of the calling function
1124 * @throws DBUnexpectedError
1125 * @return bool|ResultWrapper
1127 public function delete( $table, $conds, $fname = __METHOD__
);
1130 * INSERT SELECT wrapper. Takes data from a SELECT query and inserts it
1131 * into another table.
1133 * @param string $destTable The table name to insert into
1134 * @param string|array $srcTable May be either a table name, or an array of table names
1135 * to include in a join.
1137 * @param array $varMap Must be an associative array of the form
1138 * [ 'dest1' => 'source1', ... ]. Source items may be literals
1139 * rather than field names, but strings should be quoted with
1140 * IDatabase::addQuotes()
1142 * @param array $conds Condition array. See $conds in IDatabase::select() for
1143 * the details of the format of condition arrays. May be "*" to copy the
1146 * @param string $fname The function name of the caller, from __METHOD__
1148 * @param array $insertOptions Options for the INSERT part of the query, see
1149 * IDatabase::insert() for details.
1150 * @param array $selectOptions Options for the SELECT part of the query, see
1151 * IDatabase::select() for details.
1153 * @return ResultWrapper
1155 public function insertSelect( $destTable, $srcTable, $varMap, $conds,
1156 $fname = __METHOD__
,
1157 $insertOptions = [], $selectOptions = []
1161 * Returns true if current database backend supports ORDER BY or LIMIT for separate subqueries
1162 * within the UNION construct.
1165 public function unionSupportsOrderAndLimit();
1168 * Construct a UNION query
1169 * This is used for providing overload point for other DB abstractions
1170 * not compatible with the MySQL syntax.
1171 * @param array $sqls SQL statements to combine
1172 * @param bool $all Use UNION ALL
1173 * @return string SQL fragment
1175 public function unionQueries( $sqls, $all );
1178 * Returns an SQL expression for a simple conditional. This doesn't need
1179 * to be overridden unless CASE isn't supported in your DBMS.
1181 * @param string|array $cond SQL expression which will result in a boolean value
1182 * @param string $trueVal SQL expression to return if true
1183 * @param string $falseVal SQL expression to return if false
1184 * @return string SQL fragment
1186 public function conditional( $cond, $trueVal, $falseVal );
1189 * Returns a comand for str_replace function in SQL query.
1190 * Uses REPLACE() in MySQL
1192 * @param string $orig Column to modify
1193 * @param string $old Column to seek
1194 * @param string $new Column to replace with
1198 public function strreplace( $orig, $old, $new );
1201 * Determines how long the server has been up
1205 public function getServerUptime();
1208 * Determines if the last failure was due to a deadlock
1212 public function wasDeadlock();
1215 * Determines if the last failure was due to a lock timeout
1219 public function wasLockTimeout();
1222 * Determines if the last query error was due to a dropped connection and should
1223 * be dealt with by pinging the connection and reissuing the query.
1227 public function wasErrorReissuable();
1230 * Determines if the last failure was due to the database being read-only.
1234 public function wasReadOnlyError();
1237 * Wait for the replica DB to catch up to a given master position
1239 * @param DBMasterPos $pos
1240 * @param int $timeout The maximum number of seconds to wait for synchronisation
1241 * @return int|null Zero if the replica DB was past that position already,
1242 * greater than zero if we waited for some period of time, less than
1243 * zero if it timed out, and null on error
1245 public function masterPosWait( DBMasterPos
$pos, $timeout );
1248 * Get the replication position of this replica DB
1250 * @return DBMasterPos|bool False if this is not a replica DB.
1252 public function getSlavePos();
1255 * Get the position of this master
1257 * @return DBMasterPos|bool False if this is not a master
1259 public function getMasterPos();
1262 * @return bool Whether the DB is marked as read-only server-side
1265 public function serverIsReadOnly();
1268 * Run a callback as soon as the current transaction commits or rolls back.
1269 * An error is thrown if no transaction is pending. Queries in the function will run in
1270 * AUTO-COMMIT mode unless there are begin() calls. Callbacks must commit any transactions
1273 * This is useful for combining cooperative locks and DB transactions.
1275 * The callback takes one argument:
1276 * - How the transaction ended (IDatabase::TRIGGER_COMMIT or IDatabase::TRIGGER_ROLLBACK)
1278 * @param callable $callback
1282 public function onTransactionResolution( callable
$callback );
1285 * Run a callback as soon as there is no transaction pending.
1286 * If there is a transaction and it is rolled back, then the callback is cancelled.
1287 * Queries in the function will run in AUTO-COMMIT mode unless there are begin() calls.
1288 * Callbacks must commit any transactions that they begin.
1290 * This is useful for updates to different systems or when separate transactions are needed.
1291 * For example, one might want to enqueue jobs into a system outside the database, but only
1292 * after the database is updated so that the jobs will see the data when they actually run.
1293 * It can also be used for updates that easily cause deadlocks if locks are held too long.
1295 * Updates will execute in the order they were enqueued.
1297 * The callback takes one argument:
1298 * - How the transaction ended (IDatabase::TRIGGER_COMMIT or IDatabase::TRIGGER_IDLE)
1300 * @param callable $callback
1303 public function onTransactionIdle( callable
$callback );
1306 * Run a callback before the current transaction commits or now if there is none.
1307 * If there is a transaction and it is rolled back, then the callback is cancelled.
1308 * Callbacks must not start nor commit any transactions. If no transaction is active,
1309 * then a transaction will wrap the callback.
1311 * This is useful for updates that easily cause deadlocks if locks are held too long
1312 * but where atomicity is strongly desired for these updates and some related updates.
1314 * Updates will execute in the order they were enqueued.
1316 * @param callable $callback
1319 public function onTransactionPreCommitOrIdle( callable
$callback );
1322 * Run a callback each time any transaction commits or rolls back
1324 * The callback takes two arguments:
1325 * - IDatabase::TRIGGER_COMMIT or IDatabase::TRIGGER_ROLLBACK
1326 * - This IDatabase object
1327 * Callbacks must commit any transactions that they begin.
1329 * Registering a callback here will not affect writesOrCallbacks() pending
1331 * @param string $name Callback name
1332 * @param callable|null $callback Use null to unset a listener
1336 public function setTransactionListener( $name, callable
$callback = null );
1339 * Begin an atomic section of statements
1341 * If a transaction has been started already, just keep track of the given
1342 * section name to make sure the transaction is not committed pre-maturely.
1343 * This function can be used in layers (with sub-sections), so use a stack
1344 * to keep track of the different atomic sections. If there is no transaction,
1345 * start one implicitly.
1347 * The goal of this function is to create an atomic section of SQL queries
1348 * without having to start a new transaction if it already exists.
1350 * Atomic sections are more strict than transactions. With transactions,
1351 * attempting to begin a new transaction when one is already running results
1352 * in MediaWiki issuing a brief warning and doing an implicit commit. All
1353 * atomic levels *must* be explicitly closed using IDatabase::endAtomic(),
1354 * and any database transactions cannot be began or committed until all atomic
1355 * levels are closed. There is no such thing as implicitly opening or closing
1356 * an atomic section.
1359 * @param string $fname
1362 public function startAtomic( $fname = __METHOD__
);
1365 * Ends an atomic section of SQL statements
1367 * Ends the next section of atomic SQL statements and commits the transaction
1371 * @see IDatabase::startAtomic
1372 * @param string $fname
1375 public function endAtomic( $fname = __METHOD__
);
1378 * Run a callback to do an atomic set of updates for this database
1380 * The $callback takes the following arguments:
1381 * - This database object
1382 * - The value of $fname
1384 * If any exception occurs in the callback, then rollback() will be called and the error will
1385 * be re-thrown. It may also be that the rollback itself fails with an exception before then.
1386 * In any case, such errors are expected to terminate the request, without any outside caller
1387 * attempting to catch errors and commit anyway. Note that any rollback undoes all prior
1388 * atomic section and uncommitted updates, which trashes the current request, requiring an
1389 * error to be displayed.
1391 * This can be an alternative to explicit startAtomic()/endAtomic() calls.
1393 * @see DatabaseBase::startAtomic
1394 * @see DatabaseBase::endAtomic
1396 * @param string $fname Caller name (usually __METHOD__)
1397 * @param callable $callback Callback that issues DB updates
1398 * @return mixed $res Result of the callback (since 1.28)
1400 * @throws RuntimeException
1401 * @throws UnexpectedValueException
1404 public function doAtomicSection( $fname, callable
$callback );
1407 * Begin a transaction. If a transaction is already in progress,
1408 * that transaction will be committed before the new transaction is started.
1410 * Only call this from code with outer transcation scope.
1411 * See https://www.mediawiki.org/wiki/Database_transactions for details.
1412 * Nesting of transactions is not supported.
1414 * Note that when the DBO_TRX flag is set (which is usually the case for web
1415 * requests, but not for maintenance scripts), any previous database query
1416 * will have started a transaction automatically.
1418 * Nesting of transactions is not supported. Attempts to nest transactions
1419 * will cause a warning, unless the current transaction was started
1420 * automatically because of the DBO_TRX flag.
1422 * @param string $fname Calling function name
1423 * @param string $mode A situationally valid IDatabase::TRANSACTION_* constant [optional]
1426 public function begin( $fname = __METHOD__
, $mode = self
::TRANSACTION_EXPLICIT
);
1429 * Commits a transaction previously started using begin().
1430 * If no transaction is in progress, a warning is issued.
1432 * Only call this from code with outer transcation scope.
1433 * See https://www.mediawiki.org/wiki/Database_transactions for details.
1434 * Nesting of transactions is not supported.
1436 * @param string $fname
1437 * @param string $flush Flush flag, set to situationally valid IDatabase::FLUSHING_*
1438 * constant to disable warnings about explicitly committing implicit transactions,
1439 * or calling commit when no transaction is in progress.
1441 * This will trigger an exception if there is an ongoing explicit transaction.
1443 * Only set the flush flag if you are sure that these warnings are not applicable,
1444 * and no explicit transactions are open.
1446 * @throws DBUnexpectedError
1448 public function commit( $fname = __METHOD__
, $flush = '' );
1451 * Rollback a transaction previously started using begin().
1452 * If no transaction is in progress, a warning is issued.
1454 * Only call this from code with outer transcation scope.
1455 * See https://www.mediawiki.org/wiki/Database_transactions for details.
1456 * Nesting of transactions is not supported. If a serious unexpected error occurs,
1457 * throwing an Exception is preferrable, using a pre-installed error handler to trigger
1458 * rollback (in any case, failure to issue COMMIT will cause rollback server-side).
1460 * @param string $fname Calling function name
1461 * @param string $flush Flush flag, set to a situationally valid IDatabase::FLUSHING_*
1462 * constant to disable warnings about calling rollback when no transaction is in
1463 * progress. This will silently break any ongoing explicit transaction. Only set the
1464 * flush flag if you are sure that it is safe to ignore these warnings in your context.
1465 * @throws DBUnexpectedError
1466 * @since 1.23 Added $flush parameter
1468 public function rollback( $fname = __METHOD__
, $flush = '' );
1471 * Commit any transaction but error out if writes or callbacks are pending
1473 * This is intended for clearing out REPEATABLE-READ snapshots so that callers can
1474 * see a new point-in-time of the database. This is useful when one of many transaction
1475 * rounds finished and significant time will pass in the script's lifetime. It is also
1476 * useful to call on a replica DB after waiting on replication to catch up to the master.
1478 * @param string $fname Calling function name
1479 * @throws DBUnexpectedError
1482 public function flushSnapshot( $fname = __METHOD__
);
1485 * List all tables on the database
1487 * @param string $prefix Only show tables with this prefix, e.g. mw_
1488 * @param string $fname Calling function name
1492 public function listTables( $prefix = null, $fname = __METHOD__
);
1495 * Convert a timestamp in one of the formats accepted by wfTimestamp()
1496 * to the format used for inserting into timestamp fields in this DBMS.
1498 * The result is unquoted, and needs to be passed through addQuotes()
1499 * before it can be included in raw SQL.
1501 * @param string|int $ts
1505 public function timestamp( $ts = 0 );
1508 * Convert a timestamp in one of the formats accepted by wfTimestamp()
1509 * to the format used for inserting into timestamp fields in this DBMS. If
1510 * NULL is input, it is passed through, allowing NULL values to be inserted
1511 * into timestamp fields.
1513 * The result is unquoted, and needs to be passed through addQuotes()
1514 * before it can be included in raw SQL.
1516 * @param string|int $ts
1520 public function timestampOrNull( $ts = null );
1523 * Ping the server and try to reconnect if it there is no connection
1525 * @param float|null &$rtt Value to store the estimated RTT [optional]
1526 * @return bool Success or failure
1528 public function ping( &$rtt = null );
1531 * Get replica DB lag. Currently supported only by MySQL.
1533 * Note that this function will generate a fatal error on many
1534 * installations. Most callers should use LoadBalancer::safeGetLag()
1537 * @return int|bool Database replication lag in seconds or false on error
1539 public function getLag();
1542 * Get the replica DB lag when the current transaction started
1543 * or a general lag estimate if not transaction is active
1545 * This is useful when transactions might use snapshot isolation
1546 * (e.g. REPEATABLE-READ in innodb), so the "real" lag of that data
1547 * is this lag plus transaction duration. If they don't, it is still
1548 * safe to be pessimistic. In AUTO-COMMIT mode, this still gives an
1549 * indication of the staleness of subsequent reads.
1551 * @return array ('lag': seconds or false on error, 'since': UNIX timestamp of BEGIN)
1554 public function getSessionLagStatus();
1557 * Return the maximum number of items allowed in a list, or 0 for unlimited.
1561 public function maxListLen();
1564 * Some DBMSs have a special format for inserting into blob fields, they
1565 * don't allow simple quoted strings to be inserted. To insert into such
1566 * a field, pass the data through this function before passing it to
1567 * IDatabase::insert().
1572 public function encodeBlob( $b );
1575 * Some DBMSs return a special placeholder object representing blob fields
1576 * in result objects. Pass the object through this function to return the
1579 * @param string|Blob $b
1582 public function decodeBlob( $b );
1585 * Override database's default behavior. $options include:
1586 * 'connTimeout' : Set the connection timeout value in seconds.
1587 * May be useful for very long batch queries such as
1588 * full-wiki dumps, where a single query reads out over
1591 * @param array $options
1594 public function setSessionOptions( array $options );
1597 * Set variables to be used in sourceFile/sourceStream, in preference to the
1598 * ones in $GLOBALS. If an array is set here, $GLOBALS will not be used at
1599 * all. If it's set to false, $GLOBALS will be used.
1601 * @param bool|array $vars Mapping variable name to value.
1603 public function setSchemaVars( $vars );
1606 * Check to see if a named lock is available (non-blocking)
1608 * @param string $lockName Name of lock to poll
1609 * @param string $method Name of method calling us
1613 public function lockIsFree( $lockName, $method );
1616 * Acquire a named lock
1618 * Named locks are not related to transactions
1620 * @param string $lockName Name of lock to aquire
1621 * @param string $method Name of the calling method
1622 * @param int $timeout Acquisition timeout in seconds
1625 public function lock( $lockName, $method, $timeout = 5 );
1630 * Named locks are not related to transactions
1632 * @param string $lockName Name of lock to release
1633 * @param string $method Name of the calling method
1635 * @return int Returns 1 if the lock was released, 0 if the lock was not established
1636 * by this thread (in which case the lock is not released), and NULL if the named
1637 * lock did not exist
1639 public function unlock( $lockName, $method );
1642 * Acquire a named lock, flush any transaction, and return an RAII style unlocker object
1644 * Only call this from outer transcation scope and when only one DB will be affected.
1645 * See https://www.mediawiki.org/wiki/Database_transactions for details.
1647 * This is suitiable for transactions that need to be serialized using cooperative locks,
1648 * where each transaction can see each others' changes. Any transaction is flushed to clear
1649 * out stale REPEATABLE-READ snapshot data. Once the returned object falls out of PHP scope,
1650 * the lock will be released unless a transaction is active. If one is active, then the lock
1651 * will be released when it either commits or rolls back.
1653 * If the lock acquisition failed, then no transaction flush happens, and null is returned.
1655 * @param string $lockKey Name of lock to release
1656 * @param string $fname Name of the calling method
1657 * @param int $timeout Acquisition timeout in seconds
1658 * @return ScopedCallback|null
1659 * @throws DBUnexpectedError
1662 public function getScopedLockAndFlush( $lockKey, $fname, $timeout );
1665 * Check to see if a named lock used by lock() use blocking queues
1670 public function namedLocksEnqueue();
1673 * Find out when 'infinity' is. Most DBMSes support this. This is a special
1674 * keyword for timestamps in PostgreSQL, and works with CHAR(14) as well
1675 * because "i" sorts after all numbers.
1679 public function getInfinity();
1682 * Encode an expiry time into the DBMS dependent format
1684 * @param string $expiry Timestamp for expiry, or the 'infinity' string
1687 public function encodeExpiry( $expiry );
1690 * Decode an expiry time into a DBMS independent format
1692 * @param string $expiry DB timestamp field value for expiry
1693 * @param int $format TS_* constant, defaults to TS_MW
1696 public function decodeExpiry( $expiry, $format = TS_MW
);
1699 * Allow or deny "big selects" for this session only. This is done by setting
1700 * the sql_big_selects session variable.
1702 * This is a MySQL-specific feature.
1704 * @param bool|string $value True for allow, false for deny, or "default" to
1705 * restore the initial value
1707 public function setBigSelects( $value = true );
1710 * @return bool Whether this DB is read-only
1713 public function isReadOnly();