Method handle_message

examples/dynamic_batching.rs:115–125

(&mut self, msg: Product)

    async fn terminate(&mut self) {}

    async fn handle_message(&mut self, msg: Product) ->  ProcResult<Product> {

        // Parition_key
        let pk = match msg.ctype {
            Category::Cars => "cars".to_owned(),
            Category::Mobiles => "mobiles".to_owned(),
            Category::Accessories => "accessories".to_owned()
        };

        ProcResult::Dispatch(msg,  Some(pk))
    } 
}