Allow retrieve to pull specific version

src/documents/tests/test_api_document_versions.py

@@ -555,3 +555,23 @@ class TestDocumentVersioningApi(DirectoriesMixin, APITestCase):
 
         self.assertEqual(resp.status_code, status.HTTP_200_OK)
         self.assertEqual(resp.data["content"], "v1-content")
+
+    def test_retrieve_with_version_param_returns_selected_version_content(self) -> None:
+        root = Document.objects.create(
+            title="root",
+            checksum="root",
+            mime_type="application/pdf",
+            content="root-content",
+        )
+        v1 = Document.objects.create(
+            title="v1",
+            checksum="v1",
+            mime_type="application/pdf",
+            root_document=root,
+            content="v1-content",
+        )
+
+        resp = self.client.get(f"/api/documents/{root.id}/?version={v1.id}")
+
+        self.assertEqual(resp.status_code, status.HTTP_200_OK)
+        self.assertEqual(resp.data["content"], "v1-content")

src/documents/views.py

@@ -856,6 +856,25 @@ class DocumentViewSet(
 
         return Response({"root_id": root_doc.id})
 
+    def retrieve(
+        self,
+        request: Request,
+        *args: Any,
+        **kwargs: Any,
+    ) -> Response:
+        response = super().retrieve(request, *args, **kwargs)
+        if (
+            "version" not in request.query_params
+            or not isinstance(response.data, dict)
+            or "content" not in response.data
+        ):
+            return response
+
+        root_doc = self.get_object()
+        content_doc = self._resolve_file_doc(root_doc, request)
+        response.data["content"] = content_doc.content or ""
+        return response
+
     def update(self, request, *args, **kwargs):
         partial = kwargs.pop("partial", False)
         root_doc = self.get_object()