Feature: #75454 - Added PHP library "Doctrine DBAL" for Database Connections within TYPO3

See Issue #75454

Description

The PHP library Doctrine DBAL has been added via composer dependency to work as a powerful database abstraction layer with many features for database abstraction, schema introspection and schema management within TYPO3.

A TYPO3-specific PHP class called TYPO3\CMS\Core\Database\ConnectionPool has been added as a manager for database connections.

All connections configured below $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections'] are accessible using this manager, enabling the parallel usage of multiple database systems.

By using the database abstraction options and the QueryBuilder provided SQL statements being built will be properly quoted and compatible with different DBMS out of the box as far as possible.

Existing $GLOBALS['TYPO3_CONF_VARS']['DB'] options have been removed and/or migrated to the new Doctrine-compliant options.

Documentation for Doctrine DBAL can be found at http://www.doctrine-project.org/projects/dbal.html.

The Connection class provides convenience methods for insert, select, update, delete and truncate statements. For select, update and delete only simple equality comparisons (WHERE "aField" = 'aValue') are supported. For complex statements it's required to use the QueryBuilder.

It is possible to swap tables out of the default database and use a specific setup (e.g. for logging or caching). This snippet of a LocalConfiguration could for exampe be used to swap the sys_log table out to another database or even another database server:

//LocalConfiguration.php
//[...]
'DB' => [
    'Connections' => [
        'Default' => [
            'charset' => 'utf8',
            'dbname' => 'default_dbname',
            'driver' => 'mysqli',
            'host' => 'default_host',
            'password' => '***',
            'port' => 3306,
            'user' => 'default_user',
        ],
        'Syslog' => [
            'charset' => 'utf8',
            'dbname' => 'syslog_dbname',
            'driver' => 'mysqli',
            'host' => 'syslog_host',
            'password' => '***',
            'port' => 3306,
            'user' => 'syslog_user',
        ],
    ],
    'TableMapping' => [
        'sys_log' => 'Syslog'
    ]
],
//[...]

Impact

Currently the DatabaseConnection class only uses Doctrine to establish the database connection to MySQL, no advanced options are being used yet.

Connections always need to be requested with a table name so that the abstraction of table names to database connections stays intact.

The ConnectionPool class can be used like this:

// Get a connection which can be used for multiple operations
/** @var \TYPO3\CMS\Core\Database\Connecction $conn */
$conn = GeneralUtility::makeInstance(ConnectionPool::class)->getConnectionForTable('aTable');
$affectedRows = $conn->insert(
   'aTable',
   $fields, // Associative array of column/value pairs, automatically quoted & escaped
);
// Get a QueryBuilder, which should only be used a single time
$query = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable('aTable);
$query->select('*')
   ->from('aTable)
   ->where(
      $query->expr()->eq('aField', $query->createNamedParameter($aValue)),
      $query->expr()->lte(
         'anotherField',
         $query->createNamedParameter($anotherValue)
      )
   );
$rows = $query->execute()->fetchAll();

Extension authors are advised to use the ConnectionPool and Connection classes instead of using the Doctrine DBAL directly in order to ensure a clear upgrade path when updates to the underlying API need to be done.