the method `may_load` exists for struct `cw_storage_plus::Map<'static, (std::string::String, Uint256), Uint256>`, but its trait bounds were not satisfied the following trait bounds were not satisfied: `(std::string::String, Uint256): PrimaryKey`

[Flydexo]

Hello I have this error when I try to call may_load on a Map.
my code
let c = CARDS.may_load(deps.storage, (from, token_id))?; Ok(match c { Some(v) => { if v < value { return Err(ContractError::NoOwnCard) } }, None => return Err(ContractError::Unkown) });

[Gdowski]

Because as the error suggests, there's no implementation of a certain trait.
In this case, part of your tuple doesn't have PrimaryKey trait implemented.
Looking into documentation,
https://github.com/CosmWasm/cw-plus/blob/main/packages/storage-plus/src/keys.rs
you can see that there is an implementation for String, but not for Uint256,
as close to your desire as possible is u64.
So, either changing to u64 or implementing PrimaryKey trait for your type, is what you need :)

[maurolacy]

you can see that there is an implementation for String, but not for Uint256,
as close to your desire as possible is u64.
So, either changing to u64 or implementing PrimaryKey trait for your type, is what you need :)

That's correct. We purposely refrained for implementing PrimaryKey over u128 (and Uint256), as that would double (quadruple) the required memory layout to handle int keys (check the Key enum, in case you are interested).

You should be good to go with u64... why would you need a unique key that large? Are you planning to index the atoms in the known universe? You would still need a handful more bits for that by the way. Not to mention space requirements.

[Flydexo]

No I was using u256 because I was using solidity before and it was recommended to use u256. That's why. But yes u64 is enough.

[Flydexo]

With u64 I have the same error

[maurolacy]

Feel free to re-open and post a snippet of the failing code, and we'll take a look.

[Flydexo]

pub const CARDS: Map<(String, u64), u64> = Map::new("cards");
let c = CARDS.may_load(deps.storage,(from, token_id))?;

[maurolacy]

Works for me. What version of cw-plus are you using?

[Flydexo]

cw-storage-plus = "0.8.0"

[maurolacy]

cw-plus is now in version 0.12.1. I think you should try at least with version 0.10.x or so for this new format to work (check CHANGELOG.md, for details about IntKey deprecation).

For 0.8, using IntKey<u64> / U64Key for the integer field should work, and there should be some examples in the code base. But I seriously recommend you to update to at least v0.10.x. Or better, to the latest version.

[Flydexo]

Sorry guys but now when I try to update I recieve this error

expected a FnOnce<(std::option::Option<u64>,)> closure, found u64
the trait FnOnce<(std::option::Option<u64>,)> is not implemented for u64

With this code
let new_from_balance = CARDS.update(deps.storage, (from, token_id), q)?;

[maurolacy]

update requires a closure. You should learn to use the storage / storage-plus API.

Closing this, as this is not relevant to the original issue, nor an error or limitation in the API.