From 415593909e843a34548479ea2d3c0dbd6eee76c5 Mon Sep 17 00:00:00 2001
From: Pete Gadomski <pete.gadomski@gmail.com>
Date: Fri, 23 Jun 2023 09:48:17 -0600
Subject: [PATCH] fix: collection link should be resolved with root

Motivated by https://github.com/stac-utils/pystac-client/issues/548
---
 pystac/item.py     |  4 +++-
 tests/test_item.py | 23 ++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/pystac/item.py b/pystac/item.py
index 05837e20f..4ef676b7f 100644
--- a/pystac/item.py
+++ b/pystac/item.py
@@ -349,7 +349,9 @@ def get_collection(self) -> Optional[Collection]:
         if collection_link is None:
             return None
         else:
-            return cast(Collection, collection_link.resolve_stac_object().target)
+            return cast(
+                Collection, collection_link.resolve_stac_object(self.get_root()).target
+            )
 
     def add_derived_from(self, *items: Union[Item, str]) -> Item:
         """Add one or more items that this is derived from.
diff --git a/tests/test_item.py b/tests/test_item.py
index cc7ca2b9b..82fe681fe 100644
--- a/tests/test_item.py
+++ b/tests/test_item.py
@@ -13,7 +13,7 @@
 
 import pystac
 import pystac.serialization.common_properties
-from pystac import Asset, Catalog, Item
+from pystac import Asset, Catalog, Collection, Item, Link
 from pystac.utils import (
     datetime_to_str,
     get_opt,
@@ -586,3 +586,24 @@ def test_delete_asset_relative_no_self_link_fails(tmp_asset: pystac.Asset) -> No
     assert asset.href in str(e.value)
     assert name in item.assets
     assert os.path.exists(href)
+
+
+def test_resolve_collection_with_root(
+    tmp_path: Path, item: Item, collection: Collection
+) -> None:
+    # Motivated by https://github.com/stac-utils/pystac-client/issues/548
+    catalog = Catalog("root", "the description")
+    item.set_root(catalog)
+
+    collection_path = str(tmp_path / "collection.json")
+    collection.save_object(
+        include_self_link=False,
+        dest_href=collection_path,
+    )
+    item.add_link(Link(rel="collection", target=collection_path))
+
+    read_collection = item.get_collection()
+    assert read_collection
+    root = read_collection.get_root()
+    assert root
+    assert root.id == "root"