interact-with-a-pallet.md

title
Interact with the Nicks Pallet

Now you are ready to compile and run your node that has been enhanced with nickname capabilities from the Nicks pallet. Compile the node in release mode with:

cargo build --release

If the build fails, go back to the previous section and make sure you followed all the steps correctly. You can also view a full solution including the Nick pallet.

After the build succeeds, you can start the node:

# Run a temporary node in development mode
./target/release/node-template --dev --tmp

Start the Front-End

As in the previous tutorials, this tutorial will use the Substrate Developer Hub Front-End Template to allow you to interact with the Node Template. As long as you have completed the Create Your First Chain and Build a dApp tutorials, you should already be prepared to continue with the rest of this tutorial.

Refer directly to the front-end setup instructions for the Create Your First Chain Tutorial if necessary.

To start the Front-End Template, navigate to its directory and run:

yarn start

Use the Nicks Pallet

You should already be familiar with using the Front-End Template to interact with a pallet. In this section we will use the Nicks pallet to further illustrate how the Front-End Template can be used to interact with FRAME pallets. We will also learn more about how to use the Front-End Template to invoke privileged functions with the Sudo pallet, which is included by default as part of the Node Template. Finally, you will learn how to interpret the different types of events and errors that FRAME pallets may emit.

To get started, use the account selector from the Front-End Template to select Alice's account and then use the Pallet Interactor component to call the setName dispatchable function from the nicks pallet. You can select any name you'd like as long as it is no shorter than the MinNickLength and no longer than the MaxNickLength you configured in the previous step. Use the Signed button to execute the function.

As you can see in the image above, the Front-End Template will report the status of the dispatchable, as well as allow you to observe the events emitted by the Nicks pallet and the other pallets that compose your chain's runtime. Now use the Pallet Interactor's Query capabilities to read the value of Alice's nickname from the runtime storage of the Nicks pallet.

The return type is a tuple that contains two values: Alice's hex-encoded nickname and the amount that was reserved from Alice's account in order to secure the nickname. If you query the Nicks pallet for Bob's nickname, you'll see that the None value is returned. This is because Bob has not invoked the setName dispatchable and deposited the funds needed to reserve a nickname.

Use the Signed button to invoke the killName dispatchable function and use Bob's account ID as the function's argument. The killName function must be called by the ForceOrigin that was configured with the Nicks pallet's Config interface in the previous section. You may recall that we configured this to be the FRAME system's Root origin. The Node Template's chain specification file is used to configure the Sudo pallet to give Alice access to this origin.

The front-end template makes it easy to use the Sudo pallet to dispatch a call from the Root origin - just use the SUDO button to invoke the dispatchable. Since we just used the Signed button as opposed to the SUDO button, the function was dispatched by the Signed origin associated with Alice's account as opposed to the Root origin.

You will notice that even though the function call was successfully dispatched, a BadOrigin error was emitted and is visible in the Events pane. This means that Alice's account was still charged fees for the dispatch, but there weren't any state changes executed because the Nicks pallet follows the important verify-first-write-last pattern. Now use the SUDO button to dispatch the same call with the same parameter.

The Sudo pallet emits a Sudid event to inform network participants that the Root origin dispatched a call, however, you will notice that the inner dispatch failed with a DispatchError (the Sudo pallet's sudo function is the "outer" dispatch). In particular, this was an instance of the DispatchError::Module variant, which reports two pieces of metadata: an index number and an error number. The index number relates to the pallet from which the error originated; it corresponds with the index (position) of the pallet within the construct_runtime! macro. The error number corresponds with the index of the relevant variant from that pallet's Error enum. When using these numbers to find pallet errors, remember that the first position corresponds with index zero. In the screenshot above, the index is 9 (the tenth pallet) and the error is 2 (the third error). Depending on the position of the Nicks pallet in your construct_runtime! macro, you may see a different number for index. Regardless of the value of index, you should see that the error value is 2, which corresponds to the third variant of the Nick's pallet's Error enum, the Unnamed variant. This shouldn't be a surprise since Bob has not yet reserved a nickname, thus it cannot be cleared!

You should confirm that Alice can use the SUDO button to invoke the killName dispatchable and forcibly clear the nickname associated with any account (including her own) that actually has a nickname associated with it. Here are some other things you may want to try:

• Add a nickname that is shorter than the MinNickLength or longer than the MaxNickLength that you configured with the Nick's pallet's Config configuration trait.
• Add a nickname for Bob then use Alice's account and the SUDO button to forcibly kill Bob's nickname. Switch back to Bob's account and dispatch the clearName function.

Adding Other FRAME Pallets

In this guide, we walked through specifically how to import the Nicks pallet, but as mentioned in the beginning of this guide, each pallet will be a little different. Have no fear, you can always refer to the demonstration Substrate node runtime which includes nearly every pallet in the library of core FRAME pallets.

In the Cargo.toml file of the Substrate node runtime, you will see an example of how to import each of the different pallets, and in the lib.rs file you will see how to add each pallet to your runtime. You can generally copy what was done there as a starting point to include a pallet in your own runtime.

Learn More

• Learn how to add a more complex pallet to the Node Template by completing the Add the Contracts Pallet tutorial.
• Complete the Forkless Upgrade a Chain tutorial to learn how Substrate enables forkless runtime upgrades and follow steps to perform two upgrades, each of which is performed by way of a distinct upgrade mechanism.

References

• Nicks pallet docs