Sorting with NULL as highest, instead of lowest

This allow to sort by a field as ASC but get all null values at the end
instead of a the begining. This would typically be achieved like so:

```graphql
query {
  posts(sorting: [
    {field: title, order: ASC, nullAsHighest: true},
    {field: title, order: ASC}
  ]) {
  	title
  }
}
```

Author: PowerKiKi

src/Definition/SortingOrderType.php

@@ -7,7 +7,7 @@
 use GraphQL\Type\Definition\EnumType;
 
 /**
- * An enum for join types to be used in DQL
+ * An enum for sorting order to be used in DQL
  */
 final class SortingOrderType extends EnumType
 {

src/Factory/FilteredQueryBuilderFactory.php

@@ -176,7 +176,14 @@ private function applySorting(ClassMetadata $metadata, string $className, array
             if ($customSort) {
                 $customSort($this->uniqueNameFactory, $metadata, $this->queryBuilder, $alias, $sort['order']);
             } else {
-                $this->queryBuilder->addOrderBy($alias . '.' . $sort['field'], $sort['order']);
+                $sortingField = $alias . '.' . $sort['field'];
+                if ($sort['nullAsHighest'] ?? false) {
+                    $expression = 'CASE WHEN ' . $sortingField . ' IS NULL THEN 1 ELSE 0 END';
+                    $sortingField = $this->uniqueNameFactory->createAliasName('sorting');
+                    $this->queryBuilder->addSelect($expression . ' AS HIDDEN ' . $sortingField);
+                }
+
+                $this->queryBuilder->addOrderBy($sortingField, $sort['order']);
             }
         }
     }

src/Factory/Type/SortingTypeFactory.php

@@ -51,6 +51,12 @@ public function create(string $className, string $typeName): Type
                         'name' => 'field',
                         'type' => Type::nonNull($fieldsEnum),
                     ],
+                    [
+                        'name' => 'nullAsHighest',
+                        'type' => Type::boolean(),
+                        'description' => 'If true `NULL` values will be considered as the highest value, so appearing last in a `ASC` order, and first in a `DESC` order.',
+                        'defaultValue' => false,
+                    ],
                     [
                         'name' => 'order',
                         'type' => $this->types->get('SortingOrder'),

tests/data/ModelWithTraitsSorting.graphqls

@@ -4,6 +4,12 @@ schema {
 
 input ModelWithTraitsSorting {
   field: ModelWithTraitsSortingField!
+
+  """
+  If true `NULL` values will be considered as the highest value, so appearing
+  last in a `ASC` order, and first in a `DESC` order.
+  """
+  nullAsHighest: Boolean = false
   order: SortingOrder = ASC
 }
 

tests/data/PostSorting.graphqls

@@ -4,6 +4,12 @@ schema {
 
 input PostSorting {
   field: PostSortingField!
+
+  """
+  If true `NULL` values will be considered as the highest value, so appearing
+  last in a `ASC` order, and first in a `DESC` order.
+  """
+  nullAsHighest: Boolean = false
   order: SortingOrder = ASC
 }
 

tests/data/query-builder/sort-with-null-first.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+// all posts sorted by reversed title but with null title first
+return [
+    'SELECT post1, CASE WHEN post1.title IS NULL THEN 1 ELSE 0 END AS HIDDEN sorting1 FROM GraphQLTests\Doctrine\Blog\Model\Post post1 ORDER BY sorting1 DESC, post1.title DESC',
+    \GraphQLTests\Doctrine\Blog\Model\Post::class,
+    [],
+    [
+        [
+            'field' => 'title',
+            'nullAsHighest' => true,
+            'order' => 'DESC',
+        ],
+        [
+            'field' => 'title',
+            'order' => 'DESC',
+        ],
+    ],
+];

tests/data/query-builder/sort-with-null-last.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+// all posts sorted by title but with null title last
+return [
+    'SELECT post1, CASE WHEN post1.title IS NULL THEN 1 ELSE 0 END AS HIDDEN sorting1 FROM GraphQLTests\Doctrine\Blog\Model\Post post1 ORDER BY sorting1 ASC, post1.title ASC',
+    \GraphQLTests\Doctrine\Blog\Model\Post::class,
+    [],
+    [
+        [
+            'field' => 'title',
+            'nullAsHighest' => true,
+            'order' => 'ASC',
+        ],
+        [
+            'field' => 'title',
+            'order' => 'ASC',
+        ],
+    ],
+];