Function fetch_dbms_metadata_ddl 

pub async fn fetch_dbms_metadata_ddl<C: OracleConnection>(
    cx: &Cx,
    conn: &C,
    object_type: ObjectType,
    name: &str,
    owner: &str,
) -> Result<Option<DbmsMetadataDdl>, CatalogError>

Fetch the canonical DDL + XML representation of a single object via DBMS_METADATA.

Callers usually batch via populate_dbms_metadata_ddl which iterates every object in a CatalogSnapshot after the structural loaders have run. object_type must map to a DBMS_METADATA object type (see object_type_to_dbms_metadata_value); unknown types return an Ok(None) so the caller can continue without aborting the snapshot.