Store file:values as list of dicts in Item properties (#700)

* Store file:values as list of dicts in Item properties

* Add CHANGELOG entry for #700

CHANGELOG.md

@@ -12,6 +12,7 @@
 
 - Quickstart tutorial is now up-to-date with all package changes ([#674](https://github.com/stac-utils/pystac/pull/674))
 - Creating absolute URLs from absolute URLs ([#697](https://github.com/stac-utils/pystac/pull/697)])
+- Serialization error when using `pystac.extensions.file.MappingObject` ([#700](https://github.com/stac-utils/pystac/pull/700))
 
 ### Deprecated
 

pystac/extensions/file.py

@@ -13,7 +13,7 @@
     STACJSONDescription,
     STACVersionID,
 )
-from pystac.utils import StringEnum, get_required
+from pystac.utils import StringEnum, get_required, map_opt
 
 SCHEMA_URI = "https://stac-extensions.github.io/file/v2.0.0/schema.json"
 
@@ -83,6 +83,13 @@ def summary(self) -> str:
     def summary(self, v: str) -> None:
         self.properties["summary"] = v
 
+    @classmethod
+    def from_dict(cls, d: Dict[str, Any]) -> "MappingObject":
+        return cls.create(**d)
+
+    def to_dict(self) -> Dict[str, Any]:
+        return self.properties
+
 
 class FileExtension(
     PropertiesExtension, ExtensionManagementMixin[Union[pystac.Item, pystac.Collection]]
@@ -180,11 +187,21 @@ def values(self) -> Optional[List[MappingObject]]:
         values that are in the file and describe their meaning. See the
         :stac-ext:`Mapping Object <file#mapping-object>` docs for an example. If given,
         at least one array element is required."""
-        return self._get_property(VALUES_PROP, List[MappingObject])
+        return map_opt(
+            lambda values: [
+                MappingObject.from_dict(mapping_obj) for mapping_obj in values
+            ],
+            self._get_property(VALUES_PROP, List[Dict[str, Any]]),
+        )
 
     @values.setter
     def values(self, v: Optional[List[MappingObject]]) -> None:
-        self._set_property(VALUES_PROP, v)
+        self._set_property(
+            VALUES_PROP,
+            map_opt(
+                lambda values: [mapping_obj.to_dict() for mapping_obj in values], v
+            ),
+        )
 
     @classmethod
     def get_schema_uri(cls) -> str:

tests/extensions/test_file.py

@@ -132,11 +132,17 @@ def test_item_asset_values(self) -> None:
         item = pystac.Item.from_file(self.FILE_ITEM_EXAMPLE_URI)
         asset = item.assets["thumbnail"]
         file_ext = FileExtension.ext(asset)
-        values = [MappingObject.create([0], summary="clouds")]
+        mapping_obj = {"values": [0], "summary": "clouds"}
 
-        file_ext.values = values
+        # file_ext.values = values
+        file_ext.apply(values=[MappingObject.from_dict(mapping_obj)])
 
-        self.assertEqual(file_ext.values, values)
+        self.assertListEqual(asset.extra_fields["file:values"], [mapping_obj])
+
+        values_field = asset.extra_fields["file:values"]
+        self.assertIsInstance(values_field, list)
+        for mapping_obj in values_field:
+            self.assertIsInstance(mapping_obj, dict)
 
     def test_item_asset_apply(self) -> None:
         item = pystac.Item.from_file(self.FILE_ITEM_EXAMPLE_URI)
@@ -146,7 +152,8 @@ def test_item_asset_apply(self) -> None:
         new_checksum = "90e40210163700a8a6501eccd00b6d3b44ddaed0"
         new_size = 1
         new_header_size = 8192
-        new_values = [MappingObject.create([0], summary="clouds")]
+        new_mapping_obj = {"values": [0], "summary": "clouds"}
+        new_values = [MappingObject.from_dict(new_mapping_obj)]
         new_byte_order = ByteOrder.LITTLE_ENDIAN
 
         self.assertNotEqual(file_ext.checksum, new_checksum)
@@ -163,11 +170,11 @@ def test_item_asset_apply(self) -> None:
             values=new_values,
         )
 
-        self.assertEqual(file_ext.checksum, new_checksum)
-        self.assertEqual(file_ext.size, new_size)
-        self.assertEqual(file_ext.header_size, new_header_size)
-        self.assertEqual(file_ext.values, new_values)
-        self.assertEqual(file_ext.byte_order, new_byte_order)
+        self.assertEqual(asset.extra_fields["file:checksum"], new_checksum)
+        self.assertEqual(asset.extra_fields["file:size"], new_size)
+        self.assertEqual(asset.extra_fields["file:header_size"], new_header_size)
+        self.assertEqual(asset.extra_fields["file:values"], [new_mapping_obj])
+        self.assertEqual(asset.extra_fields["file:byte_order"], new_byte_order)
 
     def test_repr(self) -> None:
         item = pystac.Item.from_file(self.FILE_ITEM_EXAMPLE_URI)