cff: add default "message" field

* Addresses zenodo/zenodo-rdm#960

invenio_rdm_records/resources/serializers/cff/schema.py

@@ -81,6 +81,7 @@ class CFFSchema(BaseSerializerSchema):
     keywords = fields.Method("get_keywords")
     license = fields.Method("get_license")
     license_url = fields.Method("get_license_url", data_key="license-url")
+    message = fields.Method("get_message")
     # TODO references - related identifiers?
     # TODO there are other derivations of repository
     repository_code = fields.Method("get_repository_code", data_key="repository-code")
@@ -239,3 +240,13 @@ def get_type(self, obj):
             return missing
 
         return resource_type
+
+    def get_message(self, obj):
+        """Get standard citation message based on record type."""
+        resource_type = obj.get("metadata", {}).get("resource_type", {}).get("id")
+
+        type_label = "work"
+        if resource_type in self.allowed_types:
+            type_label = resource_type
+
+        return f"If you use this {type_label}, please cite it using the metadata from this file."

tests/resources/serializers/test_cff_serializer.py

@@ -55,6 +55,7 @@ def test_cff_serializer(running_app, full_record_to_dict):
         "license:\n"
         "- cc-by-4.0\n"
         "license-url: https://customlicense.org/licenses/by/4.0/\n"
+        "message: If you use this software, please cite it using the metadata from this file.\n"
         "repository-code: "
         "https://github.com/citation-file-format/cff-converter-python\n"
         "title: InvenioRDM\n"