/**
* Walks down a SelectStatement AST node, wrapping it in a COUNT (SELECT DISTINCT)
*
* Note that the ORDER BY clause is not removed. Many SQL implementations (e.g. MySQL)
* are able to cache subqueries. By keeping the ORDER BY clause intact, the limitSubQuery
* that will most likely be executed next can be read from the native SQL cache.
*
* @param SelectStatement $AST
* @return string
*/
public function walkSelectStatement(SelectStatement $AST)
{
$sql = parent::walkSelectStatement($AST);
// Find out the SQL alias of the identifier column of the root entity
// It may be possible to make this work with multiple root entities but that
// would probably require issuing multiple queries or doing a UNION SELECT
// so for now, It's not supported.
// Get the root entity and alias from the AST fromClause
$from = $AST->fromClause->identificationVariableDeclarations;
if (count($from) > 1) {
throw new \RuntimeException("Cannot count query which selects two FROM components, cannot make distinction");
}
$rootClass = $from[0]->rangeVariableDeclaration->abstractSchemaName;
$rootAlias = $from[0]->rangeVariableDeclaration->aliasIdentificationVariable;
// Get the identity properties from the metadata
$rootIdentifier = $this->queryComponents[$rootAlias]['metadata']->identifier;
// For every identifier, find out the SQL alias by combing through the ResultSetMapping
$sqlIdentifier = array();
foreach ($rootIdentifier as $property) {
foreach (array_keys($this->rsm->fieldMappings, $property) as $alias) {
if ($this->rsm->columnOwnerMap[$alias] == $rootAlias) {
$sqlIdentifier[$property] = $alias;
}
}
}
if (count($rootIdentifier) != count($sqlIdentifier)) {
throw new \RuntimeException(sprintf('Not all identifier properties can be found in the ResultSetMapping: %s', implode(', ', array_diff($rootIdentifier, array_keys($sqlIdentifier)))));
}
// Build the counter query
return sprintf('SELECT %s AS _dctrn_count FROM (SELECT DISTINCT %s FROM (%s) AS _dctrn_result) AS _dctrn_table', $this->platform->getCountExpression('*'), implode(', ', $sqlIdentifier), $sql);
}
