Introduction - Portability

Description

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 MDB2 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 factory() 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

• MDB2_PORTABILITY_ALL (default)

  turn on all portability features. this is the default setting.

• MDB2_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.

• MDB2_PORTABILITY_EMPTY_TO_NULL

  Convert empty strings values to null in data in and output. Needed because Oracle considers empty strings to be null, while most other DBMS's know the difference between empty and null.

• MDB2_PORTABILITY_ERRORS

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

  Table 33-1. Error Code Re-mappings

  Driver	Description	Old Constant	New Constant
  mysql, mysqli	unique and primary key constraints	MDB2_ERROR_ALREADY_EXISTS	MDB2_ERROR_CONSTRAINT
  mysql, mysqli	not-null constraints	MDB2_ERROR_CONSTRAINT	MDB2_ERROR_CONSTRAINT_NOT_NULL

• MDB2_PORTABILITY_FIX_ASSOC_FIELD_NAMES

  This removes any qualifiers from keys in associative fetches. some RDBMS , like for example SQLite, will be default use the fully qualified name for a column in assoc fetches if it is qualified in a query.

• MDB2_PORTABILITY_FIX_CASE

  Convert names of tables and fields to lower or upper case in all methods. The case depends on the 'field_case' option that may be set to either CASE_LOWER (default) or CASE_UPPER

• MDB2_PORTABILITY_NONE

  Turn off all portability features

• MDB2_PORTABILITY_NUMROWS

  Enable hack that makes numRows() work in Oracle

• MDB2_PORTABILITY_RTRIM

  Right trim the data output for all data fetches. This does not applied in drivers for RDBMS that automatically right trim values of fixed length character values, even if they do not right trim value of variable length character values.

Example

<?php
require_once 'MDB2.php';

$dsn = 'mysql://user:password@host/database'
$options = array(
    'debug'       => 2,
    'portability' => MDB2_PORTABILITY_NONE,
);

$mdb2 =& MDB2::connect($dsn, $options);
if (PEAR::isError($mdb2)) {
    die($mdb2->getMessage());
}
?>

<?php
// Once you have a valid MDB2 object named $mdb2...
$mdb2->setOption('field_case', CASE_LOWER);
$mdb2->setOption('portability',
        MDB2_PORTABILITY_FIX_CASE | MDB2_PORTABILITY_RTRIM);
?>

<?php
// Once you have a valid MDB2 object named $mdb2...
$mdb2->setOption('portability',
        MDB2_PORTABILITY_ALL ^ MDB2_PORTABILITY_RTRIM);
?>