Update django_mongodb_backend/schema.py

Co-authored-by: Copilot <[email protected]>

Author: aclark4life

django_mongodb_backend/schema.py

@@ -484,7 +484,10 @@ def _get_encrypted_fields_map(self, model, client, create_data_keys=False):
                 else:
                     key_doc = key_vault_collection.find_one({"keyAltNames": key_alt_name})
                     if not key_doc:
-                        raise ValueError(f"No key found in keyvault for keyAltName={key_alt_name}")
+                        raise ValueError(
+                            f"No key found in keyvault for keyAltName={key_alt_name}. "
+                            "You may need to run the management command with '--create-data-keys' to create missing keys."
+                        )
                     data_key = key_doc["_id"]
                 field_dict = {
                     "bsonType": field.db_type(connection),