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NEW Add exists as a method to the DataQuery API that will generate an SQL "exists" query

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The exists query in SQL allows the query optimiser (engine specific) to execute these queries much faster - often only needing the presence of an index to return "yes it exists".
This commit is contained in:
Guy Marriott 2019-04-15 11:14:21 +12:00 committed by Sam Minnee
parent 6b78428fbb
commit 91591373d6
2 changed files with 30 additions and 1 deletions
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2
src/ORM/DataList.php
View File

@ -963,7 +963,7 @@ class DataList extends ViewableData implements SS_List, Filterable, Sortable, Li
*/
public function exists()
{
return $this->count() > 0;
return $this->dataQuery->exists();
}
/**

29
src/ORM/DataQuery.php
View File

@ -453,6 +453,35 @@ class DataQuery
return $this->getFinalisedQuery()->count("DISTINCT {$quotedColumn}");
}
/**
* Return whether this dataquery will have records. This will use `EXISTS` statements in SQL which are more
* performant - especially when used in combination with indexed columns (that you're filtering on)
*
* @return bool
*/
public function exists()
{
// Grab a statement selecting "everything" - the engine shouldn't care what's being selected in an "EXISTS"
// statement anyway
$statement = $this->getFinalisedQuery();
$statement->setSelect('*');
// Clear limit, distinct, grouping, and order as it's not relevant for an exists query
$statement->setDistinct(false);
$statement->setOrderBy(null);
$statement->setGroupBy(null);
$statement->setLimit(null);
// Wrap the whole thing in an "EXISTS"
$sql = 'SELECT EXISTS(' . $statement->sql($params) . ')';
$result = DB::prepared_query($sql, $params);
$row = $result->first();
$result = reset($row);
// Checking for 't' supports PostgreSQL before silverstripe/postgresql@2.2
return $result === 1 || $result === 't';
}
/**
* Return the maximum value of the given field in this DataList
*