JSON:API 1.1: return empty 'included' array when ?include= is present (#1301)

* JSON:API 1.1: return empty 'included' array when ?include= is present

Fixes #1109. Ensures top-level 'included' is returned as [] when the query param
?include= is provided but no related resources exist. Updates integration tests
to reflect JSON:API v1.1 spec compliance.

* Fix tox lint environment to use setup.cfg flake8 config

* fix: ensuring empty  array is added when requested and updated tests

* Reverted unrelated changes

* Reverted unrelated tox changes

---------

Co-authored-by: Oliver Sauder <os@esite.ch>

Author: harshalkalewar

AUTHORS

@@ -15,6 +15,7 @@ David Guillot, for Contexte <dguillot@contexte.com>
 David Vogt <david.vogt@adfinis-sygroup.ch>
 Felix Viernickel <felix@gedankenspieler.org>
 Greg Aker <greg@gregaker.net>
+Harshal Kalewar <kalewarh@gmail.com>
 Humayun Ahmad <humayunahbh@gmail.com>
 Jamie Bliss <astronouth7303@gmail.com>
 Jason Housley <housleyjk@gmail.com>

CHANGELOG.md

@@ -8,6 +8,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 Note that in line with [Django REST framework policy](https://www.django-rest-framework.org/topics/release-notes/),
 any parts of the framework not mentioned in the documentation should generally be considered private API, and may be subject to change.
 
+## [Unreleased]
+
+### Fixed
+
+* Ensured that an empty `included` array is returned in responses when the `include` query parameter is present but no related resources exist.
+
 ## [8.0.0] - 2025-07-24
 
 ### Added

example/tests/integration/test_includes.py

@@ -36,7 +36,9 @@ def test_missing_field_not_included(author_bio_factory, author_factory, client):
     # First author does not have a bio
     author = author_factory(bio=None)
     response = client.get(reverse("author-detail", args=[author.pk]) + "?include=bio")
-    assert "included" not in response.json()
+    content = response.json()
+    assert "included" in content
+    assert content["included"] == []
     # Second author does
     author = author_factory()
     response = client.get(reverse("author-detail", args=[author.pk]) + "?include=bio")
@@ -204,3 +206,47 @@ def test_meta_object_added_to_included_resources(single_entry, client):
     )
     assert response.json()["included"][0].get("meta")
     assert response.json()["included"][1].get("meta")
+
+
+def test_included_array_empty_when_requested_but_no_data(blog_factory, client):
+    blog = blog_factory()
+    response = client.get(
+        reverse("blog-detail", kwargs={"pk": blog.pk}) + "?include=tags"
+    )
+    content = response.json()
+
+    assert "included" in content
+    assert content["included"] == []
+
+
+def test_included_array_populated_when_related_data_exists(
+    blog_factory, tagged_item_factory, client
+):
+    blog = blog_factory()
+    tag = tagged_item_factory(tag="django")
+    blog.tags.add(tag)
+
+    response = client.get(
+        reverse("blog-detail", kwargs={"pk": blog.pk}) + "?include=tags"
+    )
+    included = response.json()["included"]
+
+    assert included, "Expected included array to be populated"
+    assert [x.get("type") for x in included] == [
+        "taggedItems"
+    ], "Included types incorrect"
+    assert included[0]["attributes"]["tag"] == "django"
+
+
+def test_included_array_present_via_jsonapimeta_defaults(
+    single_entry, comment_factory, author_factory, client
+):
+    author = author_factory()
+    comment_factory(entry=single_entry, author=author)
+
+    response = client.get(reverse("entry-detail", kwargs={"pk": single_entry.pk}))
+
+    included = response.json()["included"]
+
+    assert included, "Expected included array due to JSONAPIMeta defaults"
+    assert any(resource["type"] == "comments" for resource in included)

example/tests/test_filters.py

@@ -530,7 +530,8 @@ def test_search_keywords(self):
                     },
                     "meta": {"bodyFormat": "text"},
                 }
-            ]
+            ],
+            "included": [],
         }
         assert response.json() == expected_result
 

rest_framework_json_api/renderers.py

@@ -652,7 +652,7 @@ def render(self, data, accepted_media_type=None, renderer_context=None):
                 if not included_cache[obj_type]:
                     del included_cache[obj_type]
 
-        if included_cache:
+        if included_resources:
             render_data["included"] = list()
             for included_type in sorted(included_cache.keys()):
                 for included_id in sorted(included_cache[included_type].keys()):