Introduction - Portability

Описание

Each database management system (DBMS) has it's own behaviors. For example, some databases capitalize field names in their output, some lowercase them, while others leave them alone. These quirks make it difficult to port your scripts over to another server type. PEAR DB strives to overcome these differences so your program can switch between DBMS's without any changes.

You control which portability modes are enabled by using the portability configuration option. Configuration options are set via connect() and setOption().

The portability modes are bitwised, so they can be combined using | and removed using ^. See the examples section below on how to do this.

Portability Mode Constants

• DB_PORTABILITY_ALL

  turn on all portability features

• DB_PORTABILITY_DELETE_COUNT

  force reporting the number of rows deleted. Some DBMS's don't count the number of rows deleted when performing simple DELETE FROM tablename queries. This mode tricks such DBMS's into telling the count by adding WHERE 1=1 to the end of DELETE queries.

• DB_PORTABILITY_ERRORS

  makes certain error messages in certain drivers compatible with those from other DBMS's

  Таблица 34-1. Error Code Re-mappings

  Driver	Description	Old Constant	New Constant
  mysql, mysqli	unique and primary key constraints	DB_ERROR_ALREADY_EXISTS	DB_ERROR_CONSTRAINT
  mysql, mysqli	not-null constraints	DB_ERROR_CONSTRAINT	DB_ERROR_CONSTRAINT_NOT_NULL
  odbc(access)	MS's ODBC driver mistakenly reports 'no such field' as code 07001, which means 'too few parameters.' When this option is on, that code gets remapped.	DB_ERROR_MISMATCH	DB_ERROR_NOSUCHFIELD

• DB_PORTABILITY_LOWERCASE

  convert names of tables and fields to lower case when using get*(), fetch*() and tableInfo()

• DB_PORTABILITY_NONE (default)

  turn off all portability features

• DB_PORTABILITY_NULL_TO_EMPTY

  convert null values to empty strings in data output by get*() and fetch*(). Needed because Oracle considers empty strings to be null, while most other DBMS's know the difference between empty and null.

• DB_PORTABILITY_NUMROWS

  enable hack that makes numRows() work in Oracle

• DB_PORTABILITY_RTRIM

  right trim the data output by get*() and fetch*()

Backwards Compatibility

Some of this functionality used to be handled by the now deprecated optimize option. For backwards compatibility, when this option is set to portability, the following databases get these portability modes turned on:

• oci8: DB_PORTABILITY_LOWERCASE and DB_PORTABILITY_DELETE_COUNT

• fbsql, mysql, mysqli, sqlite: DB_PORTABILITY_DELETE_COUNT

When the optimize option gets set to performance the portability mode is switched to DB_PORTABILITY_NONE.

Пример

<?php
require_once 'DB.php';

$dsn = 'mysql://user:password@host/database'
$options = array(
    'debug'       => 2,
    'portability' => DB_PORTABILITY_ALL,
);

$db =& DB::connect($dsn, $options);
if (PEAR::isError($db)) {
    die($db->getMessage());
}
?>

<?php
// Once you have a valid DB object named $db...
$db->setOption('portability',
        DB_PORTABILITY_LOWERCASE | DB_PORTABILITY_RTRIM);
?>

<?php
// Once you have a valid DB object named $db...
$db->setOption('portability',
        DB_PORTABILITY_ALL ^ DB_PORTABILITY_RTRIM);
?>