How to create a dynamic 'WHERE' SQL clause using TYPO3 Querybuilder - typo3

Question

How can I dynamically add extra conditions to 'WHERE' clauses in TYPO3 database queries please? The new TYPO3 Version 8 docs say how to make fixed queries, but not variable ones.
In the past, I could create a SQL statement and modify it dynamically like this:
if (condition) {
$strWhere = 'some SQL';
} else {
$strWhere = 'same SQL with extra bits';
}
$dbRes = $GLOBALS['TYPO3_DB']->exec_SELECTgetRows(
"*", // SELECT ...
"tableName", // FROM ...
$strWhere , // WHERE...
etc.
I can't see how to do something like this using Querybuilder. What I want to achieve is an expression that does something like this
if (condition) {
->where($queryBuilder->expr()->eq(... ))
}
else {
->where($queryBuilder->expr()->eq(... ))
->andWhere($queryBuilder->expr()->eq(... ))
}
Any hints would be much appreciated. Thanks.

Answer 1

Solved. My mistake was in thinking that the various parts of a Query builder statement HAVE to come together - they don't.
So this:
$queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable('tx_tablename');
$queryBuilder
->select('uid', 'header', 'bodytext')
->from('tt_content')
->where(
$queryBuilder->expr()->eq('bodytext', $queryBuilder->createNamedParameter('klaus')),
$queryBuilder->expr()->eq('header', $queryBuilder->createNamedParameter('a name'))
)
->execute();
can also be split into parts, such as:
switch ($scope) {
case 'limitfields':
$queryBuilder->select('uid','header','bodytext');
break;
default:
$queryBuilder->select('*');
break;
}
$queryBuilder
->from('tt_content')
->where(
$queryBuilder->expr()->eq('bodytext', $queryBuilder->createNamedParameter('klaus')),
$queryBuilder->expr()->eq('header', $queryBuilder->createNamedParameter('a name'))
)
->execute();

Answer 2

$queryBuilder = GeneralUtility::makeInstance('TYPO3\\CMS\\Core\\Database\\ConnectionPool')->getQueryBuilderForTable('tx_igldapssoauth_config');
$expressionBuilder = $queryBuilder->expr();
$conditions = $expressionBuilder->andX();
$conditions->add(
$expressionBuilder->eq('somefield', 1)
);
$conditions->add(
$expressionBuilder->eq('someotherfield', 2)
);
$rows = $queryBuilder->select('*')
->from('tx_igldapssoauth_config')
->where(
$queryBuilder->expr()->eq('uid', 1)
)
->andWhere($conditions)
->execute()->fetchAll();