Function path_get 

pub fn path_get(
    lhs: &Value,
    rhs: &Value,
    as_text: bool,
) -> Result<Value, EvalError>

PG json -> key / json ->> key. lhs must be JSON or TEXT containing JSON. rhs is either a TEXT key (object access) or an INT index (array access). as_text=true for ->> (returns Value::Text); false for -> (returns Value::Json).