Add roles to common metadata (#1444)

* add roles

* update changelog

* Update pystac/common_metadata.py

---------

Co-authored-by: Pete Gadomski <pete.gadomski@gmail.com>

Author: tylanderson

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Add netCDF to pystac.media_type ([#1386](https://github.com/stac-utils/pystac/pull/1386))
 - Add convenience method for accessing pystac_client ([#1365](https://github.com/stac-utils/pystac/pull/1365))
 - Fix field ordering when saving `Item`s ([#1423](https://github.com/stac-utils/pystac/pull/1423))
+- Add roles to common metadata ([#1444](https://github.com/stac-utils/pystac/pull/1444/files))
 
 ### Changed
 

pystac/common_metadata.py

@@ -213,3 +213,12 @@ def updated(self) -> datetime | None:
     @updated.setter
     def updated(self, v: datetime | None) -> None:
         self._set_field("updated", utils.map_opt(utils.datetime_to_str, v))
+
+    @property
+    def roles(self) -> list[str] | None:
+        """Get or set the semantic roles of the entity."""
+        return self._get_field("roles", list[str])
+
+    @roles.setter
+    def roles(self, v: list[str] | None) -> None:
+        self._set_field("roles", v)

tests/data-files/item/sample-item-asset-properties.json

@@ -74,6 +74,7 @@
       "start_datetime": "2017-05-01T13:22:30.040Z",
       "end_datetime": "2017-05-02T13:22:30.040Z",
       "license": "CC-BY-4.0",
+      "roles": ["a_role"],
       "providers": [
         {
           "name": "USGS",

tests/test_common_metadata.py

@@ -538,3 +538,25 @@ def test_updated(self) -> None:
         self.assertEqual(
             analytic.to_dict()["updated"], utils.datetime_to_str(set_value)
         )
+
+    def test_roles(self) -> None:
+        item = self.item.clone()
+        cm = item.common_metadata
+        analytic = item.assets["analytic"]
+        analytic_cm = CommonMetadata(analytic)
+        thumbnail = item.assets["thumbnail"]
+        thumbnail_cm = CommonMetadata(thumbnail)
+
+        item_value = cm.roles
+        a2_known_value = ["a_role"]
+
+        # Get
+        self.assertNotEqual(thumbnail_cm.roles, item_value)
+        self.assertEqual(thumbnail_cm.roles, a2_known_value)
+
+        # Set
+        set_value = ["another_role"]
+        analytic_cm.roles = set_value
+
+        self.assertEqual(analytic_cm.roles, set_value)
+        self.assertEqual(analytic.to_dict()["roles"], set_value)