TYPO3 v9: how to query additional external database (MSSQL) - typo3

Question

I am trying to query an additional external database connection in one of my repositories. In LocalConfiguration.php I've defined two connections (Default, External).
[...]
'DB' => [
'Connections' => [
// Local MySQL database
'Default' => [
// ...
],
// External MSSQL database
'External' => [
'charset' => 'utf-8',
'dbname' => 'DBNAME',
'driver' => 'sqlsrv',
'host' => 'someExternalIP',
'password' => 'somePassword',
'port' => 1433,
'user' => 'someUser',
],
],
],
[...]
In my repository I want to query the external database (via Doctrine).
$queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)
->getQueryBuilderForTable('dbo.SomeTable');
$queryBuilder->getRestrictions()->removeAll();
$queryBuilder
->select('*')
->from('dbo.SomeTable');
Do I have to explicitly tell the QueryBuilder to use that particular connection? Right now I am getting an Doctrine\DBAL\Exception\ConnectionException error, as the system tries to connect via the Default-Connection.
An exception occurred while executing 'SELECT * FROM `dbo`.`SomeTable`':
SELECT command denied to user 'myLocalUser'#'localhost' for table 'SomeTable'

Answer 1

Check out $GLOBALS['TYPO3_CONF_VARS']['DB']['TableMapping'] where you can explicitly define what tables are located in which database. See also this for some more details https://docs.typo3.org/typo3cms/CoreApiReference/ApiOverview/Database/Configuration/Index.html
The other option is actually to use ask the Connection by name, and create a query builder out of that.
GeneralUtility::makeInstance(ConnectionPool::class)->getConnectionByName('External')->createQueryBuilder(...)
I personally would go with the latter, as it is more explicit within the actual callers code what is used.

Answer 2

To work with external DB, you have to :
configure the mapping with external database and table mapping in LocalConfiguration.php
define the TCA for external tables in myExt/Configuration/TCA/MyExternalTableName.php
configure the external tables/columns mapping in ext_typoscript_setup.txt
and then, the queries in repositories will work.
Sample LocalConfiguration.php :
'DB' => [
'Connections' => [
'Default' => [
'charset' => 'utf8',
'dbname' => 'LOCAL-DB',
'driver' => 'mysqli',
'host' => '127.0.0.1',
'password' => 'PWD',
'port' => 3306,
'user' => 'USER',
],
'externalDb' => [
'charset' => 'utf8',
'dbname' => 'EXTERNAL-DB',
'driver' => 'mysqli',
'host' => 'localhost',
'password' => 'PWD',
'port' => 3306,
'user' => 'USER',
],
],
'TableMapping' => [
'MyexternalTable1' => 'externalDb',
'MyexternalTable2' => 'externalDb',
...
]
]
Sample columns mapping in myExt/ext_typoscript_setup.txt :
plugin.tx_myext {
persistence {
classes {
Vendor\MyExt\Domain\Model\LocalModel {
mapping {
tableName = ExternalTableName
recordType = \Vendor\MyExt\Domain\Model\LocalModel
columns {
col1.mapOnProperty = uid
col2.mapOnProperty = name
...
}
}
}
}
}
}