Fix nested HasOne mutations when related record exists

.claude/CLAUDE.md

@@ -85,3 +85,19 @@ Tests use `Tests\Utils\` namespace for test fixtures (Models, Queries, Mutations
 - Never use `final` in `src/`,  always in `tests/`
 - Full namespace in PHPDoc (`@var \Full\Namespace\Class`), imports in code
 - Code elements with `@api` have stability guarantees between major versions
+
+## Pull Requests
+
+Follow the [PR template](.github/PULL_REQUEST_TEMPLATE.md):
+- Link related issues
+- Add or update tests
+- Document user-facing changes in `/docs`
+- Update `CHANGELOG.md`
+
+### Changelog
+
+Add entries to the `## Unreleased` section in [CHANGELOG.md](/CHANGELOG.md).
+Use categories: `Added`, `Changed`, `Deprecated`, `Removed`, `Fixed`, `Security`.
+End each entry with a full PR URL: `https://github.com/nuwave/lighthouse/pull/<number>`.
+
+See [CONTRIBUTING.md](/CONTRIBUTING.md) for full guidelines.

CHANGELOG.md

@@ -9,6 +9,11 @@ You can find and compare releases at the [GitHub release page](https://github.co
 
 ## Unreleased
 
+### Fixed
+
+- Fix `upsert` for `HasOne` creating a new record instead of updating when no `id` is provided in the input https://github.com/nuwave/lighthouse/pull/2742
+- Throw error when using `create` on `HasOne` relation when a related model already exists https://github.com/nuwave/lighthouse/pull/2742
+
 ## v6.64.2
 
 ### Fixed

src/Execution/Arguments/NestedOneToOne.php

@@ -2,6 +2,7 @@
 
 namespace Nuwave\Lighthouse\Execution\Arguments;
 
+use GraphQL\Error\Error;
 use Illuminate\Database\Eloquent\Relations\HasOne;
 use Illuminate\Database\Eloquent\Relations\MorphOne;
 use Nuwave\Lighthouse\Support\Contracts\ArgResolver;
@@ -22,6 +23,13 @@ public function __invoke($model, $args): void
         assert($relation instanceof HasOne || $relation instanceof MorphOne);
 
         if ($args->has('create')) {
+            if ($relation->exists()) {
+                $relatedClass = class_basename($relation->getRelated());
+                $parentClass = class_basename($model);
+
+                throw new Error("Cannot create a related model: a {$relatedClass} already exists for this {$parentClass}. Use upsert to modify the existing model.");
+            }
+
             $saveModel = new ResolveNested(new SaveModel($relation));
 
             $saveModel($relation->make(), $args->arguments['create']->value);
@@ -36,7 +44,7 @@ public function __invoke($model, $args): void
         if ($args->has('upsert')) {
             $upsertModel = new ResolveNested(new UpsertModel(new SaveModel($relation)));
 
-            $upsertModel($relation->make(), $args->arguments['upsert']->value);
+            $upsertModel($relation->first() ?? $relation->make(), $args->arguments['upsert']->value);
         }
 
         if ($args->has('delete')) {

tests/Integration/Execution/MutationExecutor/HasOneTest.php

@@ -331,6 +331,42 @@ public function testUpdateWithNewHasOne(string $action): void
         ]);
     }
 
+    /** @dataProvider existingModelMutations */
+    #[DataProvider('existingModelMutations')]
+    public function testCreateHasOneWhenAlreadyExists(string $action): void
+    {
+        $task = factory(Task::class)->create();
+        $this->assertInstanceOf(Task::class, $task);
+
+        $task->post()
+            ->save(
+                factory(Post::class)->create(),
+            );
+
+        $this->graphQL(/** @lang GraphQL */ <<<GRAPHQL
+        mutation {
+            {$action}Task(input: {
+                id: 1
+                name: "foo"
+                post: {
+                    create: {
+                        title: "bar"
+                    }
+                }
+            }) {
+                id
+                name
+                post {
+                    id
+                    title
+                }
+            }
+        }
+        GRAPHQL)->assertGraphQLErrorMessage('Cannot create a related model: a Post already exists for this Task. Use upsert to modify the existing model.');
+
+        $this->assertSame(1, Post::count());
+    }
+
     /** @dataProvider existingModelMutations */
     #[DataProvider('existingModelMutations')]
     public function testUpdateAndUpdateHasOne(string $action): void
@@ -423,6 +459,54 @@ public function testUpdateAndUpsertHasOne(string $action): void
         ]);
     }
 
+    /** @dataProvider existingModelMutations */
+    #[DataProvider('existingModelMutations')]
+    public function testUpdateAndUpsertExistingHasOneWithoutID(string $action): void
+    {
+        $task = factory(Task::class)->create();
+        $this->assertInstanceOf(Task::class, $task);
+
+        $task->post()
+            ->save(
+                factory(Post::class)->create(),
+            );
+
+        $this->graphQL(/** @lang GraphQL */ <<<GRAPHQL
+        mutation {
+            {$action}Task(input: {
+                id: 1
+                name: "foo"
+                post: {
+                    upsert: {
+                        title: "bar"
+                    }
+                }
+            }) {
+                id
+                name
+                post {
+                    id
+                    title
+                }
+            }
+        }
+        GRAPHQL)->assertJson([
+            'data' => [
+                "{$action}Task" => [
+                    'id' => '1',
+                    'name' => 'foo',
+                    'post' => [
+                        'id' => '1',
+                        'title' => 'bar',
+                    ],
+                ],
+            ],
+        ]);
+
+        // Assert that the existing post was updated, not a new one created
+        $this->assertSame(1, Post::count());
+    }
+
     /** @dataProvider existingModelMutations */
     #[DataProvider('existingModelMutations')]
     public function testUpdateAndDeleteHasOne(string $action): void