How to use Mapping with Sha2x256 in ink smart contracts

Question

I want to try and use Mapping with Sha2x256 or any other value that is large enough so that each of these will be unique.

I want mapping to be like this: unique_ids: Mapping <Sha2x256 ,u128>

Whenever I try to make Mapping <String, u128> I get an error "contract doesn't have a size known at compile-time"

So I'm trying anything else that can act as an unique id and will not repeat itself. It can be Sha2x256, Blake2s256 etc.

Does anyone have any advice?

Answer 1

You can't use String in ink! to store data because String processing comes with a lot of overhead and alternatively you can use Vec<u8> instead and if you really need String you can use ink_prelude::String view the link. You can go through this Question for further details