use enum values and fix fields pydantic validation

CHANGES.md

@@ -2,6 +2,15 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- use Relation's `value` for `POST` prev/next links
+- return `JSONResponse` directly from `/items` endpoint when `fields` parameter is pass and avoid Pydantic validation
+
+### Changed
+
+- avoid re-use of internal `CoreCrudClient.post_search` in `CoreCrudClient.get_search` method to allow customization
+
 ## [4.0.1] - 2025-02-06
 
 ### Added

stac_fastapi/pgstac/core.py

@@ -393,15 +393,28 @@ async def item_collection(
             sortby=sortby,
         )
 
-        search_request = self.pgstac_search_model(**clean)
+        try:
+            search_request = self.pgstac_search_model(**clean)
+        except ValidationError as e:
+            raise HTTPException(
+                status_code=400, detail=f"Invalid parameters provided {e}"
+            ) from e
+
         item_collection = await self._search_base(search_request, request=request)
 
         links = await ItemCollectionLinks(
             collection_id=collection_id, request=request
         ).get_links(extra_links=item_collection["links"])
         item_collection["links"] = links
 
-        return item_collection
+        # If we have the `fields` extension enabled
+        # we need to avoid Pydantic validation because the
+        # Items might not be a valid STAC Item objects
+        if fields := getattr(search_request, "fields", None):
+            if fields.include or fields.exclude:
+                return JSONResponse(item_collection)  # type: ignore
+
+        return ItemCollection(**item_collection)
 
     async def get_item(
         self, item_id: str, collection_id: str, request: Request, **kwargs
@@ -500,15 +513,23 @@ async def get_search(
             filter_lang=filter_lang,
         )
 
-        # Do the request
         try:
             search_request = self.pgstac_search_model(**clean)
         except ValidationError as e:
             raise HTTPException(
                 status_code=400, detail=f"Invalid parameters provided {e}"
             ) from e
 
-        return await self.post_search(search_request, request=request)
+        item_collection = await self._search_base(search_request, request=request)
+
+        # If we have the `fields` extension enabled
+        # we need to avoid Pydantic validation because the
+        # Items might not be a valid STAC Item objects
+        if fields := getattr(search_request, "fields", None):
+            if fields.include or fields.exclude:
+                return JSONResponse(item_collection)  # type: ignore
+
+        return ItemCollection(**item_collection)
 
     def _clean_search_args(  # noqa: C901
         self,

stac_fastapi/pgstac/models/links.py

@@ -140,8 +140,8 @@ def link_next(self) -> Optional[Dict[str, Any]]:
 
             if method == "POST":
                 return {
-                    "rel": Relations.next,
-                    "type": MimeTypes.geojson,
+                    "rel": Relations.next.value,
+                    "type": MimeTypes.geojson.value,
                     "method": method,
                     "href": f"{self.request.url}",
                     "body": {**self.request.postbody, "token": f"next:{self.next}"},
@@ -164,8 +164,8 @@ def link_prev(self) -> Optional[Dict[str, Any]]:
 
             if method == "POST":
                 return {
-                    "rel": Relations.previous,
-                    "type": MimeTypes.geojson,
+                    "rel": Relations.previous.value,
+                    "type": MimeTypes.geojson.value,
                     "method": method,
                     "href": f"{self.request.url}",
                     "body": {**self.request.postbody, "token": f"prev:{self.prev}"},

tests/resources/test_item.py

@@ -1072,6 +1072,13 @@ async def test_field_extension_get(app_client, load_test_data, load_test_collect
     )
     assert resp.status_code == 201
 
+    params = {"fields": "+properties.proj:epsg,+properties.gsd,+collection"}
+    resp = await app_client.get(
+        f"/collections/{test_item['collection']}/items", params=params
+    )
+    feat_properties = resp.json()["features"][0]["properties"]
+    assert not set(feat_properties) - {"proj:epsg", "gsd", "datetime"}
+
     params = {"fields": "+properties.proj:epsg,+properties.gsd,+collection"}
     resp = await app_client.get("/search", params=params)
     feat_properties = resp.json()["features"][0]["properties"]