the trait bound `Vec<u8>: EncodeLike<u32>` is not satisfied

Question

I was making a function to store the some data in the pallet. #[pallet::storage] #[pallet::getter(fn number)] // Learn more about declaring storage items: // https://docs.substrate.io/main-docs/build/runtime-storage/#declaring-storage-items

pub type Number<T> = StorageMap<_, Blake2_128Concat,u32,Vec<u8>,ValueQuery>;

#[pallet::weight(10_000 + T::DbWeight::get().writes(1).ref_time())]
        pub fn store_data(origin: OriginFor<T>, number: u32, data: Vec<u8>) -> DispatchResult {
            // Check that the extrinsic was signed and get the signer.
            // This function will return an error if the extrinsic is not signed.
            // https://docs.substrate.io/main-docs/build/origins/
            let who = ensure_signed(origin)?;

            // Update storage.
            <Number<T>>::insert(number,data.clone());

            // Emit an event.
            Self::deposit_event(Event::SomethingStored ( who.clone(),number.clone(),data.clone() ));
            // Return a successful DispatchResultWithPostInfo
            Ok(())
        }

And i was making a function in which i want to print the current existing data of the particular storage.

    #[pallet::weight(10_000 + T::DbWeight::get().writes(1).ref_time())]
    pub fn show_data(origin: OriginFor<T>,number: u32, data: Vec<u8> ) -> DispatchResult {
        // Check that the extrinsic was signed and get the signer.
        // This function will return an error if the extrinsic is not signed.
        let who = ensure_signed(origin)?;
    
        // Update storage.
         <Number<T>>::get(number);
        <Number<T>>::get(data.clone());
    
    
        // Emit an event.
        Self::deposit_event(Event::Data(who.clone(),number.clone(),data.clone()));
    
        Ok(())
    }

In the number(u32) is working fine. But in the get(Vec) is showing the trait EncodeLike<u32> is not implemented for Vec<u8>

Answer 1

The StorageValue Number is a data structure similar to traditional hash maps with key-to-value mapping (See the docs).

The method get loads the value associated with the given key from the map.

fn get<KeyArg: EncodeLike<K>>(key: KeyArg) -> Self::Query

And the insert stores a value to be associated with the given key from the map:

fn insert<KeyArg: EncodeLike<K>, ValArg: EncodeLike<V>>(key: KeyArg, val: ValArg)

Therefore in your case it makes sense to retrieve the value from the number, because you are storing number as a key:

<Number<T>>::insert(number,data.clone());
let data_from_storage = <Number<T>>::get(number);

But you can not do it the other way around (retrieve the key from the data)

    <Number<T>>::get(data.clone());

This will work in case you want to use the Vec as a Key and the number as a Value (But not sure if it makes sense):

#[pallet::storage]
#[pallet::getter(fn number)]
pub type Number<T> = StorageMap<_, Blake2_128Concat,Vec<u8>, u32, ValueQuery>;

Then use Vec as a key:

<Number<T>>::insert(data.clone(), number);

And you can retrieve the number:

let number_from_storage = <Number<T>>::get(data.clone());