diff --git a/.docs/filters.md b/.docs/filters.md
index e1e741d0..afbd24fd 100644
--- a/.docs/filters.md
+++ b/.docs/filters.md
@@ -90,6 +90,16 @@ $grid->addFilterText('custom', 'Custom search:', 'name')
 	});
 ```
 
+
+When using `NetteDatabaseDataSource`, the callback receives the data source instance. Use `addWhereCondition()` to append raw SQL conditions:
+
+```php
+$grid->addFilterText('custom', 'Custom search:', 'name')
+	->setCondition(function(NetteDatabaseDataSource $dataSource, $value) {
+		$dataSource->addWhereCondition('id > ?', [strlen($value)]);
+	});
+```
+
 ### Templates:
 
 Filters can also have their own templates:
diff --git a/src/DataSource/NetteDatabaseDataSource.php b/src/DataSource/NetteDatabaseDataSource.php
index ae63dc65..3c6a4ee4 100644
--- a/src/DataSource/NetteDatabaseDataSource.php
+++ b/src/DataSource/NetteDatabaseDataSource.php
@@ -110,9 +110,9 @@ public function sort(Sorting $sorting): IDataSource
 		return $this;
 	}
 
-	public function getDataSource(): Explorer
+	public function getDataSource(): NetteDatabaseDataSource
 	{
-		return $this->connection;
+		return $this;
 	}
 
 	/**
@@ -128,7 +128,7 @@ public function getQuery(): array
 	/**
 	 * @param mixed[] $params
 	 */
-	protected function addWhereCondition(string $sql, array $params = []): void
+	public function addWhereCondition(string $sql, array $params = []): void
 	{
 		$this->whereConditions[] = [$sql, $params];
 	}
diff --git a/tests/Cases/DataSources/NetteDatabaseDataSourceTest.phpt b/tests/Cases/DataSources/NetteDatabaseDataSourceTest.phpt
index f4d46b51..c5d9176e 100644
--- a/tests/Cases/DataSources/NetteDatabaseDataSourceTest.phpt
+++ b/tests/Cases/DataSources/NetteDatabaseDataSourceTest.phpt
@@ -167,7 +167,7 @@ final class NetteDatabaseDataSourceTest extends BaseDataSourceTest
 	public function testGetDataSource(): void
 	{
 		$s = new NetteDatabaseDataSource($this->db, 'SELECT * FROM users');
-		Assert::same($this->db, $s->getDataSource());
+		Assert::same($s, $s->getDataSource());
 	}
 
 	public function testGetDataCached(): void
@@ -308,6 +308,21 @@ final class NetteDatabaseDataSourceTest extends BaseDataSourceTest
 		Assert::same(['%John%', '%John%'], $params);
 	}
 
+	public function testCustomWhereCondition(): void
+	{
+		$s = new NetteDatabaseDataSource($this->db, 'SELECT * FROM users');
+		$filter = new FilterText($this->grid, 'a', 'b', []);
+		$filter->setValue('text');
+		$filter->setCondition(function (NetteDatabaseDataSource $dataSource, $value): void {
+			$dataSource->addWhereCondition('id > ?', [strlen($value)]);
+		});
+		$s->filter([$filter]);
+		[$sql, $params] = $s->getQuery();
+
+		Assert::same('SELECT * FROM (SELECT * FROM users) AS datagrid_base WHERE id > ?', $sql);
+		Assert::same([4], $params);
+	}
+
 	protected function setUpDatabase(): void
 	{
 		$connection = new Connection('sqlite::memory:');