Kitty Counter

Let's now learn how to use our new StorageValue.

Basic APIs

This tutorial will only go over just the basic APIs needed to build our Pallet.

Check out the StorageValue documentation if you want to see the full APIs.

Reading Storage

To read the current value of a StorageValue, you can simply call the get API:

#![allow(unused)]
fn main() {
let maybe_count: Option<u32> = CountForKitties::<T>::get();
}

A few things to note here.

The most obvious one is that get returns an Option, rather than the type itself.

In fact, all storage in a blockchain is an Option: either there is some data in the database or there isn't.

In this context, when there is no value in storage for the CountForKitties, we probably mean that the CountForKitties is zero.

So we can write the following to handle this ergonomically:

#![allow(unused)]
fn main() {
let current_count: u32 = CountForKitties::<T>::get().unwrap_or(0);
}

Now, whenever CountForKitties returns Some(count), we will simply unwrap that count and directly access the u32. If it returns None, we will simply return 0u32 instead.

The other thing to note is the generic <T> that we need to include. You better get used to this, we will be using <T> everywhere! But remember, in our definition of CountForKitties, it was a type generic over <T: Config>, and thus we need to include <T> to access any of the APIs.

Writing Storage

To set the current value of a StorageValue, you can simply call the set API:

#![allow(unused)]
fn main() {
CountForKitties::<T>::set(Some(1u32));
}

This storage API cannot fail, so there is no error handling needed. You just set the value directly in storage. Note that set will also happily replace any existing value there, so you will need to use other APIs like exists or get to check if a value is already in storage.

If you set the storage to None, it is the same as deleting the storage item.

Your Turn

Now that you know the basics of reading and writing to storage, add the logic needed to increment the CountForKitties storage whenever we call mint.

#![allow(unused)]
fn main() {
use super::*;
use frame::prelude::*;

impl<T: Config> Pallet<T> {
	pub fn mint(owner: T::AccountId) -> DispatchResult {
		/* 🚧 TODO 🚧:
			- `get` the `current_count` of kitties.
			- `unwrap_or` set the count to `0`.
			- Create `new_count` by adding one to the `current_count`.
			- `set` the `new_count` of kitties.
		*/
		Self::deposit_event(Event::<T>::Created { owner });
		Ok(())
	}
}
}
#![allow(unused)]
fn main() {
use super::*;
use frame::prelude::*;

impl<T: Config> Pallet<T> {
	pub fn mint(owner: T::AccountId) -> DispatchResult {
		let current_count: u32 = CountForKitties::<T>::get().unwrap_or(0);
		let new_count = current_count + 1;
		CountForKitties::<T>::set(Some(new_count));
		Self::deposit_event(Event::<T>::Created { owner });
		Ok(())
	}
}
}
#![allow(unused)]
fn main() {
// Tests for the Kitties Pallet.
//
// Normally this file would be split into two parts: `mock.rs` and `tests.rs`.
// The `mock.rs` file would contain all the setup code for our `TestRuntime`.
// Then `tests.rs` would only have the tests for our pallet.
// However, to minimize the project, these have been combined into this single file.
//
// Learn more about creating tests for Pallets:
// https://paritytech.github.io/polkadot-sdk/master/polkadot_sdk_docs/guides/your_first_pallet/index.html

// This flag tells rust to only run this file when running `cargo test`.
#![cfg(test)]

use crate as pallet_kitties;
use crate::*;
use frame::deps::sp_io;
use frame::runtime::prelude::*;
use frame::testing_prelude::*;
use frame::traits::fungible::*;

type Balance = u64;
type Block = frame_system::mocking::MockBlock<TestRuntime>;

// In our "test runtime", we represent a user `AccountId` with a `u64`.
// This is just a simplification so that we don't need to generate a bunch of proper cryptographic
// public keys when writing tests. It is just easier to say "user 1 transfers to user 2".
// We create the constants `ALICE` and `BOB` to make it clear when we are representing users below.
const ALICE: u64 = 1;
const BOB: u64 = 2;

// Our blockchain tests only need 3 Pallets:
// 1. System: Which is included with every FRAME runtime.
// 2. PalletBalances: Which is manages your blockchain's native currency. (i.e. DOT on Polkadot)
// 3. PalletKitties: The pallet you are building in this tutorial!
construct_runtime! {
	pub struct TestRuntime {
		System: frame_system,
		PalletBalances: pallet_balances,
		PalletKitties: pallet_kitties,
	}
}

// Normally `System` would have many more configurations, but you can see that we use some macro
// magic to automatically configure most of the pallet for a "default test configuration".
#[derive_impl(frame_system::config_preludes::TestDefaultConfig)]
impl frame_system::Config for TestRuntime {
	type Block = Block;
	type AccountData = pallet_balances::AccountData<Balance>;
}

// Normally `pallet_balances` would have many more configurations, but you can see that we use some
// macro magic to automatically configure most of the pallet for a "default test configuration".
#[derive_impl(pallet_balances::config_preludes::TestDefaultConfig)]
impl pallet_balances::Config for TestRuntime {
	type AccountStore = System;
	type Balance = Balance;
}

// This is the configuration of our Pallet! If you make changes to the pallet's `trait Config`, you
// will also need to update this configuration to represent that.
impl pallet_kitties::Config for TestRuntime {
	type RuntimeEvent = RuntimeEvent;
}

// We need to run most of our tests using this function: `new_test_ext().execute_with(|| { ... });`
// It simulates the blockchain database backend for our tests.
// If you forget to include this and try to access your Pallet storage, you will get an error like:
// "`get_version_1` called outside of an Externalities-provided environment."
pub fn new_test_ext() -> sp_io::TestExternalities {
	frame_system::GenesisConfig::<TestRuntime>::default()
		.build_storage()
		.unwrap()
		.into()
}

#[test]
fn starting_template_is_sane() {
	new_test_ext().execute_with(|| {
		let event = Event::<TestRuntime>::Created { owner: ALICE };
		let _runtime_event: RuntimeEvent = event.into();
		let _call = Call::<TestRuntime>::create_kitty {};
		let result = PalletKitties::create_kitty(RuntimeOrigin::signed(BOB));
		assert_ok!(result);
	});
}

#[test]
fn system_and_balances_work() {
	// This test will just sanity check that we can access `System` and `PalletBalances`.
	new_test_ext().execute_with(|| {
		// We often need to set `System` to block 1 so that we can see events.
		System::set_block_number(1);
		// We often need to add some balance to a user to test features which needs tokens.
		assert_ok!(PalletBalances::mint_into(&ALICE, 100));
		assert_ok!(PalletBalances::mint_into(&BOB, 100));
	});
}

#[test]
fn create_kitty_checks_signed() {
	new_test_ext().execute_with(|| {
		// The `create_kitty` extrinsic should work when being called by a user.
		assert_ok!(PalletKitties::create_kitty(RuntimeOrigin::signed(ALICE)));
		// The `create_kitty` extrinsic should fail when being called by an unsigned message.
		assert_noop!(PalletKitties::create_kitty(RuntimeOrigin::none()), DispatchError::BadOrigin);
	})
}

#[test]
fn create_kitty_emits_event() {
	new_test_ext().execute_with(|| {
		// We need to set block number to 1 to view events.
		System::set_block_number(1);
		// Execute our call, and ensure it is successful.
		assert_ok!(PalletKitties::create_kitty(RuntimeOrigin::signed(ALICE)));
		// Assert the last event by our blockchain is the `Created` event with the correct owner.
		System::assert_last_event(Event::<TestRuntime>::Created { owner: 1 }.into());
	})
}

#[test]
fn count_for_kitties_created_correctly() {
	new_test_ext().execute_with(|| {
		// Querying storage before anything is set will return `None`.
		assert_eq!(CountForKitties::<TestRuntime>::get(), None);
		// You can `set` the value using an `Option<u32>`.
		CountForKitties::<TestRuntime>::set(Some(1337u32));
		// You can `put` the value directly with a `u32`.
		CountForKitties::<TestRuntime>::put(1337u32);
		// Check that the value is now in storage.
		assert_eq!(CountForKitties::<TestRuntime>::get(), Some(1337u32));
	})
}

#[test]
fn mint_increments_count_for_kitty() {
	new_test_ext().execute_with(|| {
		// Querying storage before anything is set will return `None`.
		assert_eq!(CountForKitties::<TestRuntime>::get(), None);
		// Call `create_kitty` which will call `mint`.
		assert_ok!(PalletKitties::create_kitty(RuntimeOrigin::signed(ALICE)));
		// Now the storage should be `Some(1)`
		assert_eq!(CountForKitties::<TestRuntime>::get(), Some(1));
	})
}
}
diff --git a/src/impls.rs b/src/impls.rs
index 03abf99..b396f98 100644
--- a/src/impls.rs
+++ b/src/impls.rs
@@ -3,6 +3,12 @@ use frame::prelude::*;
 
 impl<T: Config> Pallet<T> {
 	pub fn mint(owner: T::AccountId) -> DispatchResult {
+		/* 🚧 TODO 🚧:
+			- `get` the `current_count` of kitties.
+			- `unwrap_or` set the count to `0`.
+			- Create `new_count` by adding one to the `current_count`.
+			- `set` the `new_count` of kitties.
+		*/
 		Self::deposit_event(Event::<T>::Created { owner });
 		Ok(())
 	}
diff --git a/src/impls.rs b/src/impls.rs
index b396f98..9739330 100644
--- a/src/impls.rs
+++ b/src/impls.rs
@@ -3,12 +3,9 @@ use frame::prelude::*;
 
 impl<T: Config> Pallet<T> {
 	pub fn mint(owner: T::AccountId) -> DispatchResult {
-		/* 🚧 TODO 🚧:
-			- `get` the `current_count` of kitties.
-			- `unwrap_or` set the count to `0`.
-			- Create `new_count` by adding one to the `current_count`.
-			- `set` the `new_count` of kitties.
-		*/
+		let current_count: u32 = CountForKitties::<T>::get().unwrap_or(0);
+		let new_count = current_count + 1;
+		CountForKitties::<T>::set(Some(new_count));
 		Self::deposit_event(Event::<T>::Created { owner });
 		Ok(())
 	}
diff --git a/src/tests.rs b/src/tests.rs
index 7713826..6de2fcc 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -131,3 +131,15 @@ fn count_for_kitties_created_correctly() {
 		assert_eq!(CountForKitties::<TestRuntime>::get(), Some(1337u32));
 	})
 }
+
+#[test]
+fn mint_increments_count_for_kitty() {
+	new_test_ext().execute_with(|| {
+		// Querying storage before anything is set will return `None`.
+		assert_eq!(CountForKitties::<TestRuntime>::get(), None);
+		// Call `create_kitty` which will call `mint`.
+		assert_ok!(PalletKitties::create_kitty(RuntimeOrigin::signed(ALICE)));
+		// Now the storage should be `Some(1)`
+		assert_eq!(CountForKitties::<TestRuntime>::get(), Some(1));
+	})
+}