/**
* The new SQL store's implementation of query answering. This function
* works in two stages: First, the nested conditions of the given query
* object are preprocessed to compute an abstract representation of the
* SQL query that is to be executed. Since query conditions correspond to
* joins with property tables in most cases, this abstract representation
* is essentially graph-like description of how property tables are joined.
* Moreover, this graph is tree-shaped, since all query conditions are
* tree-shaped. Each part of this abstract query structure is represented
* by an QuerySegment object in the array m_queries.
*
* As a second stage of processing, the thus prepared SQL query is actually
* executed. Typically, this means that the joins are collapsed into one
* SQL query to retrieve results. In some cases, such as in dbug mode, the
* execution might be restricted and not actually perform the whole query.
*
* The two-stage process helps to separate tasks, and it also allows for
* better optimisations: it is left to the execution engine how exactly the
* query result is to be obtained. For example, one could pre-compute
* partial suib-results in temporary tables (or even cache them somewhere),
* instead of passing one large join query to the DB (of course, it might
* be large only if the configuration of SMW allows it). For some DBMS, a
* step-wise execution of the query might lead to better performance, since
* it exploits the tree-structure of the joins, which is important for fast
* processing -- not all DBMS might be able in seeing this by themselves.
*
* @param Query $query
*
* @return mixed depends on $query->querymode
*/
public function getQueryResult(Query $query)
{
if ((!$this->engineOptions->get('smwgIgnoreQueryErrors') || $query->getDescription() instanceof ThingDescription) && $query->querymode != Query::MODE_DEBUG && count($query->getErrors()) > 0) {
return new QueryResult($query->getDescription()->getPrintrequests(), $query, array(), $this->store, false);
// NOTE: we check this here to prevent unnecessary work, but we check
// it after query processing below again in case more errors occurred.
} elseif ($query->querymode == Query::MODE_NONE) {
// don't query, but return something to printer
return new QueryResult($query->getDescription()->getPrintrequests(), $query, array(), $this->store, true);
}
$db = $this->store->getConnection('mw.db');
$this->queryMode = $query->querymode;
$this->querySegmentList = array();
$this->errors = array();
QuerySegment::$qnum = 0;
$this->sortKeys = $query->sortkeys;
// *** First compute abstract representation of the query (compilation) ***//
$this->querySegmentListBuilder->setSortKeys($this->sortKeys);
$this->querySegmentListBuilder->buildQuerySegmentFor($query->getDescription());
// compile query, build query "plan"
$qid = $this->querySegmentListBuilder->getLastQuerySegmentId();
$this->querySegmentList = $this->querySegmentListBuilder->getQuerySegmentList();
$this->errors = $this->querySegmentListBuilder->getErrors();
if ($qid < 0) {
// no valid/supported condition; ensure that at least only proper pages are delivered
$qid = QuerySegment::$qnum;
$q = new QuerySegment();
$q->joinTable = SMWSql3SmwIds::TABLE_NAME;
$q->joinfield = "{$q->alias}.smw_id";
$q->where = "{$q->alias}.smw_iw!=" . $db->addQuotes(SMW_SQL3_SMWIW_OUTDATED) . " AND {$q->alias}.smw_iw!=" . $db->addQuotes(SMW_SQL3_SMWREDIIW) . " AND {$q->alias}.smw_iw!=" . $db->addQuotes(SMW_SQL3_SMWBORDERIW) . " AND {$q->alias}.smw_iw!=" . $db->addQuotes(SMW_SQL3_SMWINTDEFIW);
$this->querySegmentList[$qid] = $q;
}
if (isset($this->querySegmentList[$qid]->joinTable) && $this->querySegmentList[$qid]->joinTable != SMWSql3SmwIds::TABLE_NAME) {
// manually make final root query (to retrieve namespace,title):
$rootid = QuerySegment::$qnum;
$qobj = new QuerySegment();
$qobj->joinTable = SMWSql3SmwIds::TABLE_NAME;
$qobj->joinfield = "{$qobj->alias}.smw_id";
$qobj->components = array($qid => "{$qobj->alias}.smw_id");
$qobj->sortfields = $this->querySegmentList[$qid]->sortfields;
$this->querySegmentList[$rootid] = $qobj;
} else {
// not such a common case, but worth avoiding the additional inner join:
$rootid = $qid;
}
// Include order conditions (may extend query if needed for sorting):
if ($this->engineOptions->get('smwgQSortingSupport')) {
$this->applyOrderConditions($rootid);
}
// Possibly stop if new errors happened:
if (!$this->engineOptions->get('smwgIgnoreQueryErrors') && $query->querymode != Query::MODE_DEBUG && count($this->errors) > 0) {
$query->addErrors($this->errors);
return new QueryResult($query->getDescription()->getPrintrequests(), $query, array(), $this->store, false);
}
// *** Now execute the computed query ***//
$this->querySegmentListProcessor->setQueryMode($this->queryMode);
$this->querySegmentListProcessor->setQuerySegmentList($this->querySegmentList);
// execute query tree, resolve all dependencies
$this->querySegmentListProcessor->doExecuteSubqueryJoinDependenciesFor($rootid);
switch ($query->querymode) {
case Query::MODE_DEBUG:
$result = $this->getDebugQueryResult($query, $rootid);
break;
case Query::MODE_COUNT:
$result = $this->getCountQueryResult($query, $rootid);
break;
default:
$result = $this->getInstanceQueryResult($query, $rootid);
break;
}
$this->querySegmentListProcessor->cleanUp();
$query->addErrors($this->errors);
return $result;
}
