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Create and use a storage Map

Learn how to write into a storage map.


Learn how to use a StorageMap using FRAME V2's syntax.

Use cases#

Declaring a Storage Map and using it in a pallet.


We will create 2 maps :

  • WhenLastSomethingDone : to store the lastest block number when a function is called
  • CallsCounterBySender : to store a counter by sender address for a function called


1. Define a StorageMap instance#

Use FRAME's StorageMap to declare the struct as a new single item in storage:

#[pallet::getter(fn when_last_something_done)]
pub type WhenLastSomethingDone<T: Config> = StorageMap<_, Twox64Concat, T::AccountId, T::BlockNumber, ValueQuery>;
#[pallet::getter(fn call_counter_by_sender)]
pub type CallsCounterBySender<T: Config> = StorageMap<_, Twox64Concat, T::AccountId, u32, ValueQuery>;

2. Write to the WhenLastSomethingDone storage item#

Example of using WhenLastSomethingDone inside a function using insert :

let who = ensure_signed(origin)?;
let now = frame_system::Pallet::<T>::block_number();
<WhenLastSomethingDone<T>>::insert(&who, now);

3. Write to the CallsCounterBySender storage item#

Example of the CallsCounterBySender StorageMap being used inside a function:

let who = ensure_signed(origin)?;
if ! <CallsCounterBySender<T>>::contains_key(&who) {
<CallsCounterBySender<T>>::insert(&who, 0);
let counter = <CallsCounterBySender<T>>::get(&who).saturating_add(1);
<CallsCounterBySender<T>>::insert(&who, counter);



Rust docs#

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