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Getting the error:

the trait MaxEncodedLen is not implemented for SomeStruct

If I add MaxEncodedLen to the #[derive()] list it changes to this:

error[E0599]: no function or associated item named max_encoded_len found for struct frame_support::dispatch::Vec<u8> in the current scope --> /home/aely/substrate-node-template/pallets/template/src/lib.rs:42:9

How do I store a struct that has a Vec or is a string in js?

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2 Answers 2

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This is what ended up working.

How to store a string in substrate storage?

Instead of using

Struct {
    string_field: Vec<u8>
}

Using:

Struct {
   string_field: [u8; some_limit]
}

I also had to import MaxEncodedLength and add it to the #[derive()] list as well.

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use can use BoundedVec<u8, ConstU32<128>> instead using the Vec<8> in the struct . if you need to use struct into the storage you have to use this macro with the storage :

#[pallet::unbounded]

Exmaple :

#[pallet::storage]
#[pallet::unbounded]
#[pallet::getter(fn storage)]
pub(super) type storage<T: Config> = StorageDoubleMap<
    _,
    Twox64Concat,
    HashId<T>,
    Twox64Concat,
    AccountOf<T>,
    /*struct*/,
    OptionQuery,
>;

The BoundedVec<u8, ConstU32<128>> type signifies a vector of u8 elements with a bounded length, in this case, a maximum length of 128 elements. This construct is typical in Substrate-based blockchains to put an upper limit on the size of dynamic collections to ensure that they do not grow indefinitely, which could lead to performance issues or exploits.

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