How to store a string in substrate storage?

Question

I would like to store a string/message in substrate storage because I am writing a pallet, later on, I would like to use the Polkadot.js portal to write the message on the front-end and store it, and then later to react it.

Does Polkadot.js convert Vec to string automatically? If not how can I test it? Thank you!

Answer 1

Yes, the way to go is to store it as Vec<u8> and to use a BoundedVec to limit the max number of chars in order to not let users store the entire internet in your pallet.

The nicks pallet is a perfect starting point for you to explore this as it has this exact functionality to map readable strings to addresses.

Here is the storage config: https://github.com/paritytech/substrate/blob/master/frame/nicks/src/lib.rs#L112-L114

And here is the associated extrinsic:

https://github.com/paritytech/substrate/blob/master/frame/nicks/src/lib.rs#L139-L158

Yes, it's converted by polkadot.js into string!

Answer 2

String is represented as Vec. So in your fn put vec parameter

Answer 3

Use arrays to store your String because arrays work great with those struct macros below...(BoundedVec will not work with most of them):

    #[derive(Default, Encode, Decode, Clone, MaxEncodedLen, PartialEq, RuntimeDebug, TypeInfo)]
    pub struct UserInfo {
        pub id: i64,
        pub username: [u8; 20],
    //BoundedVec<u8, T::StringLimit>,
    }

In your function argument, take input strings in Vec type, then pad the vector into arrays. See here: https://stackoverflow.com/questions/71578765/best-way-to-pad-a-vector-with-zero-bytes

Also you can get the expected string size from pallet Config:

let expected_len = T::StringLimit::get() as usize;