Last updated 2024-09-10

Write a smart contract

Now that you have a unique namespace controlled by your administrative keyset, you're ready to start building the backend for the election application. In this tutorial, you'll learn the basics of how to write a smart contract that can be deployed on the blockchain as the backend code for the election application.

A smart contract is a special type of application runs automatically when the conditions specified in the contract logic are met. By deploying a smart contract on a blockchain, the terms of an agreement can be executed programmatically in a decentralized way, without any intermediary involvement or process delays.

On the Kadena blockchain, a smart contract consists of one or more modules written in the Pact programming language. For this tutorial, the election smart contract consists of two modules: the main election module and an auxiliary gas station module.

The exercises in this tutorial illustrate the basics of building and deploying a Pact module as you develop the main election module. At the completion of this tutorial, you'll deploy the core logic of the election module on your local development network.

Before you begin

Before you start this tutorial, verify the following basic requirements:

You have an internet connection and a web browser installed on your local computer.
You have a code editor, such as Visual Studio Code, access to an interactive terminal shell, and are generally familiar with using command-line programs.
You have cloned the voting-dapp repository to create your project directory as described in Prepare your workspace.
You have the development network running in a Docker container as described in Start a local blockchain.
You are connected to the development network using your local host IP address and port number 8080.
You have created and funded an administrative account as described in Add an administrator account.
You have created a principal namespace on the development network as described in Define a namespace.
You have defined the keyset that controls your namespace using the administrative account as described in Define keysets.

Define a minimal Pact module

To get started writing Pact modules, you must have a file that contains the bare minimum of code required to deploy. You can create and test this starter code for a Pact module using the Pact REPL. After you have a minimal working deployment, you can add and refactor the code to add functionality to the Pact module.

To create the starter code for a Pact module:

Open the election-dapp/pact folder in the code editor on your computer.
Create a new file named module.repl in the pact folder.

Add a transaction that defines a module named election by typing the following lines of code in the module.repl file:

(begin-tx  "Deploy the election module")  (module election)(commit-tx)

(begin-tx  "Deploy the election module")  (module election)(commit-tx)

Execute the transaction using the pact command-line program running locally or using pact-cli from the Docker container.

If pact-cli is installed locally, run the following command inside the pact folder in the terminal shell:
```
pact module.repl --trace
```
```
pact module.repl --trace
```
As before, if you don't have pact installed locally, you can load the module.repl file in the pact-cli from the Docker container with the following command:
```
(load "module.repl")
```
```
(load "module.repl")
```
If you are using the pact-cli in a browser, you can replace the pact module.repl --trace command with (load "module.repl") throughout this tutorial.

You'll see that this transaction fails with an error similar to the following:
```
error: Unexpected end of input, Expected: atom, Expected: literal
```
```
error: Unexpected end of input, Expected: atom, Expected: literal
```
Modules require you to define either a keyset or a capability to protect access to the module's functions. Capabilities are similar to keysets in that they control permissions—who can do what—in the context of a Pact smart contract. You'll learn more about capabilities in this tutorial and in other tutorials. For now, you can use the admin-keyset you defined in the previous tutorial.
Add the admin-keyset to the transaction to define the election module in the module.repl file:
```
(begin-tx  "Deploy the election module")  (module election "election.admin-keyset")(commit-tx)
```
```
(begin-tx  "Deploy the election module")  (module election "election.admin-keyset")(commit-tx)
```
If you execute the transaction in the Pact REPL now, you'll see a different error:
```
error: Unexpected end of input, Expected: list
```
```
error: Unexpected end of input, Expected: list
```
Although you've added an owner to the module, the module doesn't yet include any functions. You must define at least one function in a Pact module for the module to be valid.
Add a list-candidates function inside the transaction that defines the election module.
```
(begin-tx  "Deploy the election module")  (module election "election.admin-keyset"    (defun list-candidates () [])  )(commit-tx)
```
```
(begin-tx  "Deploy the election module")  (module election "election.admin-keyset"    (defun list-candidates () [])  )(commit-tx)
```
Later, you'll update this function to list the candidates stored in a database table. For now, this function just returns an empty list ([]). If you execute the transaction in the Pact REPL now, you should see a familiar error:
```
Error: No such keyset: 'election.admin-keyset
```
```
Error: No such keyset: 'election.admin-keyset
```
Remember that you can only define a keyset in a namespace. The current module.repl file doesn't define a namespace, so it can't define or use the keyset you've specified for the module definition.

Add the following code—which should look familiar from the previous tutorials—before the transaction to define the election module:

(env-data  { 'admin-keyset :    { 'keys : [ 'admin-key ]    , 'pred : 'keys-all    }  })(env-sigs  [{ 'key  : 'admin-key   , 'caps : []  }]) (begin-tx  "Define a namespace for the module")  (define-namespace 'election (read-keyset 'admin-keyset) (read-keyset 'admin-keyset))(commit-tx)(begin-tx  "Define a keyset to govern the module")  (namespace 'election)  (define-keyset "election.admin-keyset" (read-keyset 'admin-keyset))(commit-tx)

(env-data  { 'admin-keyset :    { 'keys : [ 'admin-key ]    , 'pred : 'keys-all    }  })(env-sigs  [{ 'key  : 'admin-key   , 'caps : []  }]) (begin-tx  "Define a namespace for the module")  (define-namespace 'election (read-keyset 'admin-keyset) (read-keyset 'admin-keyset))(commit-tx)(begin-tx  "Define a keyset to govern the module")  (namespace 'election)  (define-keyset "election.admin-keyset" (read-keyset 'admin-keyset))(commit-tx)

As you might remember from previous tutorials, this code:

Loads the admin-keyset context and signatures into the REPL environment.
Defines the election namespace.
Enters the election namespace to define the election.admin-keyset as the namespace owner.

Execute the transaction using the pact command-line program:

pact module.repl --trace

pact module.repl --trace

You'll now see that the transaction succeeds with output similar to the following:

module.repl:1:0:Trace: Setting transaction datamodule.repl:9:0:Trace: Setting transaction signatures/capsmodule.repl:15:0:Trace: Begin Tx 0: Define a namespace for the modulemodule.repl:18:4:Trace: Namespace defined: electionmodule.repl:19:0:Trace: Commit Tx 0: Define a namespace for the modulemodule.repl:21:0:Trace: Begin Tx 1: Define a keyset to govern the modulemodule.repl:24:4:Trace: Namespace set to electionmodule.repl:25:4:Trace: Keyset definedmodule.repl:26:0:Trace: Commit Tx 1: Define a keyset to govern the modulemodule.repl:28:0:Trace: Begin Tx 2: Deploy the election modulemodule.repl:31:4:Trace: Loaded module election, hash ElJ6iBzJbN_WaWuzr6PPPVkjlCQAXhosymHnI3nPYZMmodule.repl:34:0:Trace: Commit Tx 2: Deploy the election moduleLoad successful

module.repl:1:0:Trace: Setting transaction datamodule.repl:9:0:Trace: Setting transaction signatures/capsmodule.repl:15:0:Trace: Begin Tx 0: Define a namespace for the modulemodule.repl:18:4:Trace: Namespace defined: electionmodule.repl:19:0:Trace: Commit Tx 0: Define a namespace for the modulemodule.repl:21:0:Trace: Begin Tx 1: Define a keyset to govern the modulemodule.repl:24:4:Trace: Namespace set to electionmodule.repl:25:4:Trace: Keyset definedmodule.repl:26:0:Trace: Commit Tx 1: Define a keyset to govern the modulemodule.repl:28:0:Trace: Begin Tx 2: Deploy the election modulemodule.repl:31:4:Trace: Loaded module election, hash ElJ6iBzJbN_WaWuzr6PPPVkjlCQAXhosymHnI3nPYZMmodule.repl:34:0:Trace: Commit Tx 2: Deploy the election moduleLoad successful

You now have all of the starter code required to define the Pact election module in the election namespace. The module is governed by the election.admin-keyset and only includes one function.

Test the election module

Although the election module is governed by a keyset and can't be modified without a signed transaction, the list-candidate function is publicly accessible. You can use the global list-modules Pact function in the Pact REPL to test access to the election module and the list-candidate function.

To test access to the election module:

Open the election-dapp/pact/module.repl file in the code editor on your computer.

Add the following transaction to assert that the election module is available:

(begin-tx   "Look up the election module")  (expect   "The election module should exist"   ["election"]   (list-modules)  )(commit-tx)

(begin-tx   "Look up the election module")  (expect   "The election module should exist"   ["election"]   (list-modules)  )(commit-tx)

Execute the transaction using the pact command-line program:

pact module.repl --trace

pact module.repl --trace

You should see output similar to the following that indicates the election module is defined in the Pact REPL:

module.repl:35:0:Trace: Begin Tx 3: Look up the election modulemodule.repl:38:3:Trace: Expect: success: The election module should existmodule.repl:43:1:Trace: Commit Tx 3: Look up the election moduleLoad successful

module.repl:35:0:Trace: Begin Tx 3: Look up the election modulemodule.repl:38:3:Trace: Expect: success: The election module should existmodule.repl:43:1:Trace: Commit Tx 3: Look up the election moduleLoad successful

Add the following lines of code to the module.repl file to clear the environment keyset and signature information, call the list-candidates function on the election module, and assert that the function returns an empty array:

(env-data {})(env-sigs [])(begin-tx  "Call list-candidates")  (expect    "list-candidates returns an empty list"    []    (election.list-candidates)  )(commit-tx)

(env-data {})(env-sigs [])(begin-tx  "Call list-candidates")  (expect    "list-candidates returns an empty list"    []    (election.list-candidates)  )(commit-tx)

Execute the transaction using the pact command-line program:

pact module.repl --trace

pact module.repl --trace

You should see output similar to the following that indicates you were able to call the list-candidates function without signing the transaction and that the function returned an empty list:

module.repl:44:0:Trace: Setting transaction datamodule.repl:45:0:Trace: Setting transaction signatures/capsmodule.repl:47:0:Trace: Begin Tx 4: Call list-candidatesmodule.repl:50:5:Trace: Expect: success: list-candidates returns an empty listmodule.repl:55:0:Trace: Commit Tx 4: Call list-candidatesLoad successful

module.repl:44:0:Trace: Setting transaction datamodule.repl:45:0:Trace: Setting transaction signatures/capsmodule.repl:47:0:Trace: Begin Tx 4: Call list-candidatesmodule.repl:50:5:Trace: Expect: success: list-candidates returns an empty listmodule.repl:55:0:Trace: Commit Tx 4: Call list-candidatesLoad successful

Proving that you can call this function inside of the election module without an identity context or a signature is important because, in a democracy, the list of candidates should be publicly accessible.

Update the election Pact module

When you defined the election module, you specified the keyset used to govern it. Every change to the module requires the update transaction to be signed with that keyset. To test that updates work as expected, you can try updating the Pact module with the correct keyset and with an incorrect keyset.

Use the correct keyset

To test updating a module with the correct keyset:

Open the election-dapp/pact/module.repl file in the code editor on your computer.

Add the following lines of code after the last transaction:

(env-data  { 'admin-keyset :    { 'keys : [ 'admin-key ]    , 'pred : 'keys-all    }  })(env-sigs  [{ 'key  : 'admin-key   , 'caps : []  }])(begin-tx  "Update the module")  (module election "election.admin-keyset"    (defun list-candidates () [1, 2, 3])  )(commit-tx)(begin-tx  "Call updated list-candidates function")  (expect    "list-candidates returns a list with numbers"    [1, 2, 3]    (election.list-candidates)  )(commit-tx)

(env-data  { 'admin-keyset :    { 'keys : [ 'admin-key ]    , 'pred : 'keys-all    }  })(env-sigs  [{ 'key  : 'admin-key   , 'caps : []  }])(begin-tx  "Update the module")  (module election "election.admin-keyset"    (defun list-candidates () [1, 2, 3])  )(commit-tx)(begin-tx  "Call updated list-candidates function")  (expect    "list-candidates returns a list with numbers"    [1, 2, 3]    (election.list-candidates)  )(commit-tx)

This code:

Reloads the correct keyset and signature into the Pact REPL.
Redefines the election module with the list-candidates function to return a list containing 1, 2, 3.
Tests that list-candidates returns the new list.

Execute the transaction using the pact command-line program:

pact module.repl --trace

pact module.repl --trace

You should see output similar to the following that indicates you were able to call the updated list-candidates function and that the function returned a list with numbers:

module.repl:82:0:Trace: Begin Tx 6: Call updated list-candidates functionmodule.repl:85:4:Trace: Expect: success: list-candidates returns a list with numbersmodule.repl:90:0:Trace: Commit Tx 6: Call updated list-candidates functionLoad successful

module.repl:82:0:Trace: Begin Tx 6: Call updated list-candidates functionmodule.repl:85:4:Trace: Expect: success: list-candidates returns a list with numbersmodule.repl:90:0:Trace: Commit Tx 6: Call updated list-candidates functionLoad successful

Use an incorrect keyset

You can't use expect-failure in the Pact REPL to test module definitions, but you can simulate an unauthorized user attempting to update a module.

To test updating a module with an incorrect keyset:

Open the election-dapp/pact/module.repl file in the code editor on your computer.

Add the following lines of code after the last transaction:

(env-data  { 'admin-keyset :    { 'keys : [ 'other-key ]    , 'pred : 'keys-all    }  })(env-sigs  [{ 'key  : 'other-key   , 'caps : []  }])(begin-tx  "Upgrade the module without permission")    (module election "election.admin-keyset"      (defun list-candidates () [])    )(commit-tx)

(env-data  { 'admin-keyset :    { 'keys : [ 'other-key ]    , 'pred : 'keys-all    }  })(env-sigs  [{ 'key  : 'other-key   , 'caps : []  }])(begin-tx  "Upgrade the module without permission")    (module election "election.admin-keyset"      (defun list-candidates () [])    )(commit-tx)

Execute the transaction using the pact command-line program:
```
pact module.repl --trace
```
```
pact module.repl --trace
```
You should see the Load failed message and that the failure was caused by a Keyset failure error. With these two tests, you know that you can update the Pact module by signing a transaction with the election.admin-keyset and that no other keyset can update the election module.
Remove the code you added for testing an incorrect keyset.
Execute the transaction using the pact command-line program to verify that the module.repl file loads successfully before you continue:
```
pact module.repl --trace
```
```
pact module.repl --trace
```

Modify module governance

You now have the basic scaffolding for the election module in place. However, your current configuration uses the election.admin-keyset to govern the election module and its functions. To simplify permission management with a separation of concerns, you can use a capability to control access to the module instead of using the election.admin-keyset keyset directly. By moving module ownership to a governance capability, you can later use the election.admin-keyset keyset to restrict access to specific functions without repeating code.

To modify governance for the module:

Open the election-dapp/pact/module.repl file in the code editor on your computer.

Add the following lines of code after the last transaction:

(env-data  { 'admin-keyset :    { 'keys : [ 'admin-key ]    , 'pred : 'keys-all    }  })(env-sigs  [{ 'key  : 'admin-key   , 'caps : []  }]) (begin-tx  "Refactor governance of the module")  (module election GOVERNANCE   (defcap GOVERNANCE ()      (enforce-keyset "election.admin-keyset"))    (defun list-candidates () [1, 2, 3])  )(commit-tx)

(env-data  { 'admin-keyset :    { 'keys : [ 'admin-key ]    , 'pred : 'keys-all    }  })(env-sigs  [{ 'key  : 'admin-key   , 'caps : []  }]) (begin-tx  "Refactor governance of the module")  (module election GOVERNANCE   (defcap GOVERNANCE ()      (enforce-keyset "election.admin-keyset"))    (defun list-candidates () [1, 2, 3])  )(commit-tx)

This code resets the environment and defines a GOVERNANCE capability that enforces the use of the election.admin-keyset keyset when called upon.

Execute the transaction using the pact command-line program:

pact module.repl --trace

pact module.repl --trace

You should see output similar to the following that indicates you successfully updated the election module to be governed by a capability:

module.repl:106:0:Trace: Begin Tx 7: Refactor governance of the modulemodule.repl:109:4:Trace: Loaded module election, hash QIk-zRAVReFt6NAFNhdEjXOVYRhqlKsGDH8q0-gB0sAmodule.repl:114:0:Trace: Commit Tx 7: Refactor governance of the moduleLoad successful

module.repl:106:0:Trace: Begin Tx 7: Refactor governance of the modulemodule.repl:109:4:Trace: Loaded module election, hash QIk-zRAVReFt6NAFNhdEjXOVYRhqlKsGDH8q0-gB0sAmodule.repl:114:0:Trace: Commit Tx 7: Refactor governance of the moduleLoad successful

You can write additional test cases to verify that the election.admin-keyset is still able to update the module now that governance of the module is implemented with a capability.

Deploy the Pact module locally

Now that you've seen how to define and update a Pact module, you're ready to deploy the module on the local development network with the administrative account you created using Chainweaver.

To deploy the Pact module on the development network:

Verify the development network is currently running on your local computer.
Open and unlock the Chainweaver desktop or web application and verify that:
- You're connected to development network (devnet) from the network list.
- Your administrative account name with the k: prefix exists on chain 1.
- Your administrative account name is funded with KDA on chain 1.
You're going to use Chainweaver to sign the transaction that deploys the module.
Open the election-dapp/pact folder in the code editor on your computer.
Create a new file named election.pact in the pact folder.

Add the minimal Pact code required to define a module to the election.pact file.

Remember that a module definition requires a namespace, a governing owner, and at least one function.

Because you're deploying the module in your own principal namespace on the local development network, replace the generic election namespace and keyset you used in the module.repl file with the unique principal namespace you defined on the development network.

For example:

(namespace 'n_14912521e87a6d387157d526b281bde8422371d1) (module election GOVERNANCE  (defcap GOVERNANCE ()    (enforce-keyset "n_14912521e87a6d387157d526b281bde8422371d1.admin-keyset"))   (defun list-candidates () [1, 2, 3]))

(namespace 'n_14912521e87a6d387157d526b281bde8422371d1) (module election GOVERNANCE  (defcap GOVERNANCE ()    (enforce-keyset "n_14912521e87a6d387157d526b281bde8422371d1.admin-keyset"))   (defun list-candidates () [1, 2, 3]))

Open the election-dapp/snippets/deploy-module.ts file in your code editor.

You'll notice several differences between this script and the previous scripts you've used. For example, in this script, the Pact code is read from your election.pact module rather than passed as a string or a function call to an existing module like Pact.modules.coin.
```
async function main(account: string, upgrade: boolean) {  const transaction = Pact.builder    .execution(fs.readFileSync('../pact/election.pact', 'utf8'))
```
```
async function main(account: string, upgrade: boolean) {  const transaction = Pact.builder    .execution(fs.readFileSync('../pact/election.pact', 'utf8'))
```
You'll also see that the metadata for the transaction specifies a gas limit and gas price:
```
gasLimit: 100000,gasPrice: 0.00000001,
```
```
gasLimit: 100000,gasPrice: 0.00000001,
```
Deploying a Pact module is a relatively expensive type of transaction because of the resources required to update the blockchain. The transaction will fail if the gas limit is set too low.

After the code used to sign the transaction, the script sends a preflight request for the signed transaction to the blockchain using the Kadena client. The response to the preflight request contains information about the expected success of the transaction and the how much gas the transaction requires. The preflight request helps to ensure that the script doesn't send a transaction to the blockchain that is likely to fail.

Because you must for pay processing any transaction request even if a transaction fails, you should use a preflight request for any computationally expensive transactions—like deploying a module—before sending the actual transaction to the blockchain.
Open the election-dapp/snippets folder in a terminal shell on your computer.
Deploy your election module on the development network by running a command similar to the following with your administrative account name:
```
npm run deploy-module:devnet -- k:<your-public-key>
```
```
npm run deploy-module:devnet -- k:<your-public-key>
```
Remember that k:<your-public-key> is the default account name for the administrative account that you funded in Add an administrator account. You can copy this account name from Chainweaver when viewing the account watch list. When you run the script, you should see Chainweaver display a QuickSign Request.

Click Sign All to sign the request.

After you click Sign All, the transaction is executed and the results are displayed in your terminal shell. For example, you should see output similar to the following:

{  gas: 60322,  result: {    status: 'success',    data: 'Loaded module n_14912521e87a6d387157d526b281bde8422371d1.election, hash U76LNmIBivLHjDUq3CADxeMQG5iPO7vaFF84ROMSeXA'  },  reqKey: 'RAGwn_Jf67lOIISXsNy6qXbBqlN4sVxt8v8B9q6hLxw',  logs: 'A42hBn7VEdDxa4vuhuLd0D3R0MzNQMI-hXaJVVcmVwg',  events: [    {      params: [Array],      name: 'TRANSFER',      module: [Object],      moduleHash: 'M1gabakqkEi_1N8dRKt4z5lEv1kuC_nxLTnyDCuZIK0'    }  ],  metaData: {    publicMeta: {      creationTime: 1705011524,      ttl: 28800,      gasLimit: 100000,      chainId: '1',      gasPrice: 1e-8,      sender: 'k:5ec41b89d323398a609ffd54581f2bd6afc706858063e8f3e8bc76dc5c35e2c0'    },    blockTime: 1705011521970026,    prevBlockHash: 'oJhZZ8m00vBdH4z8_siE1gbHhb4aUE0W2G9uB2QSlHQ',    blockHeight: 996  },  continuation: null,  txId: 1014,  preflightWarnings: []}{  status: 'success',  data: 'Loaded module n_14912521e87a6d387157d526b281bde8422371d1.election, hash U76LNmIBivLHjDUq3CADxeMQG5iPO7vaFF84ROMSeXA'}

{  gas: 60322,  result: {    status: 'success',    data: 'Loaded module n_14912521e87a6d387157d526b281bde8422371d1.election, hash U76LNmIBivLHjDUq3CADxeMQG5iPO7vaFF84ROMSeXA'  },  reqKey: 'RAGwn_Jf67lOIISXsNy6qXbBqlN4sVxt8v8B9q6hLxw',  logs: 'A42hBn7VEdDxa4vuhuLd0D3R0MzNQMI-hXaJVVcmVwg',  events: [    {      params: [Array],      name: 'TRANSFER',      module: [Object],      moduleHash: 'M1gabakqkEi_1N8dRKt4z5lEv1kuC_nxLTnyDCuZIK0'    }  ],  metaData: {    publicMeta: {      creationTime: 1705011524,      ttl: 28800,      gasLimit: 100000,      chainId: '1',      gasPrice: 1e-8,      sender: 'k:5ec41b89d323398a609ffd54581f2bd6afc706858063e8f3e8bc76dc5c35e2c0'    },    blockTime: 1705011521970026,    prevBlockHash: 'oJhZZ8m00vBdH4z8_siE1gbHhb4aUE0W2G9uB2QSlHQ',    blockHeight: 996  },  continuation: null,  txId: 1014,  preflightWarnings: []}{  status: 'success',  data: 'Loaded module n_14912521e87a6d387157d526b281bde8422371d1.election, hash U76LNmIBivLHjDUq3CADxeMQG5iPO7vaFF84ROMSeXA'}

You now have a smart contract with one election module governed by the admin-keyset deployed in your principal namespace on your local development network. You can verify that your module is deployed by running the following command:

npm run list-modules:devnet

npm run list-modules:devnet

You should see output similar to the following:

[  'coin',  'fungible-v1',  'fungible-v2',  'fungible-xchain-v1',  'gas-payer-v1',  'n_14912521e87a6d387157d526b281bde8422371d1.election',  'ns']

[  'coin',  'fungible-v1',  'fungible-v2',  'fungible-xchain-v1',  'gas-payer-v1',  'n_14912521e87a6d387157d526b281bde8422371d1.election',  'ns']

View smart contract modules in Chainweaver

After you deploy a module, you can use Chainweaver to view and interact with it.

To view the module in Chainweaver:

Open and unlock the Chainweaver desktop or web application.
In Chainweaver, click Contracts in the navigation panel, then click Module Explorer.
Under Deployed Contracts, click Refresh, then search for the election module.
Click View to see the name of the function and capability that you defined in the module.
Click Open to see the content of the module in the editor panel.

The line specifying the namespace for the module isn't included because it isn't considered part of the module itself.
Click Call to the right of the list-candidates function.
In the Function: list-candidates window, click Preview and scroll down to see that the Raw Response displayed is [1, 2, 3].

This is an actual response from the blockchain that you can receive without paying any transaction fees.

In certain situations, getting a raw response is a preferable alternative to sending an transaction to the blockchain because sending a transaction requires you to pay for processing of the transaction.
Leave Chainweaver open with the content of the election module displayed.

Update your deployed Pact module

Being able to update a deployed smart contract is an important part of building applications on the Kadena network. Many blockchain projects don't allow smart contracts to be updated after they have been deployed on the public blockchain. With Kadena, you can build and deploy iteratively so you can add new features and fix bugs as your application matures.

To test updating a deployed smart contract:

Open the election-dapp/pact/election.pact file in the code editor on your computer.

Modify the list-candidates function to return a different list. For example:

  (defun list-candidates () [1, 2, 3, 4, 5])

  (defun list-candidates () [1, 2, 3, 4, 5])

Open the election-dapp/snippets folder in a terminal shell on your computer.

Update the election module by running the deploy-module:devnet script:

npm run deploy-module:devnet -- k:<your-public-key>

npm run deploy-module:devnet -- k:<your-public-key>

Click Sign All in Chainweaver to sign the request.
In Chainweaver, click Open to refresh the module and confirm that the module displays the changes you made.
Click Call to the right of the list-candidates function, click Preview and scroll to see that the Raw Response from the blockchain now displays the changes you made for the return value of the function.

Verify other accounts can't update your module

You've seen that you can use your account to deploy and update the election module on the local development network. You might also want to verify that no other accounts can make changes to your deployed module.

To verify that other accounts can't update your module:

In Chainweaver, click Keys in the navigation panel.
Click Generate Key to add a new public key to your list of public keys.
Click Add k: Account for the new public key to add a new account to the list of accounts you are watching.
Copy the Account name for the new account.
Open the election-dapp/snippets folder in a terminal shell on your computer.
Create and fund the new account using the transfer-create script by running a command similar to the following with the new account name you copied from Chainweaver:
```
npm run transfer-create:devnet -- <new-account-name>
```
```
npm run transfer-create:devnet -- <new-account-name>
```
Attempt to update the election module by running the deploy-module script with the new account name you copied from Chainweaver:
```
npm run deploy-module:devnet -- <new-account-name>
```
```
npm run deploy-module:devnet -- <new-account-name>
```

Click Sign All in Chainweaver to sign the request using the new account key.

You should see that the transaction fails with output similar to the following:

{  gas: 100000,  result: {    status: 'failure',    error: {      callStack: [],      type: 'TxFailure',      message: "Keyset failure (keys-all): 'n_14912521e87a6d387157d526b281bde8422371d1.admin-keyset",      info: ''    }  },  reqKey: 'Bk61YLKYVx6lv2HiHtTonpppoVwiz3iiroQtMYEa2XI',  logs: 'cNEOIFujnGkxkEMnfh9oFCek13XvxAqHq4truHweGYg',  events: [    {      params: [Array],      name: 'TRANSFER',      module: [Object],      moduleHash: 'M1gabakqkEi_1N8dRKt4z5lEv1kuC_nxLTnyDCuZIK0'    }  ],  metaData: {    publicMeta: {      creationTime: 1705016898,      ttl: 28800,      gasLimit: 100000,      chainId: '1',      gasPrice: 1e-8,      sender: 'k:99d30af3fa91d78cc06cf53a0d4eb2d7fa2a5a72944cc5451311b455a67a3c1c'    },    blockTime: 1705016899793480,    prevBlockHash: 'LbPeMhAF-hLbpG76FO9DJQLtapRtg3ITyHRDpqec1wg',    blockHeight: 2016  },  continuation: null,  txId: null,  preflightWarnings: []}

{  gas: 100000,  result: {    status: 'failure',    error: {      callStack: [],      type: 'TxFailure',      message: "Keyset failure (keys-all): 'n_14912521e87a6d387157d526b281bde8422371d1.admin-keyset",      info: ''    }  },  reqKey: 'Bk61YLKYVx6lv2HiHtTonpppoVwiz3iiroQtMYEa2XI',  logs: 'cNEOIFujnGkxkEMnfh9oFCek13XvxAqHq4truHweGYg',  events: [    {      params: [Array],      name: 'TRANSFER',      module: [Object],      moduleHash: 'M1gabakqkEi_1N8dRKt4z5lEv1kuC_nxLTnyDCuZIK0'    }  ],  metaData: {    publicMeta: {      creationTime: 1705016898,      ttl: 28800,      gasLimit: 100000,      chainId: '1',      gasPrice: 1e-8,      sender: 'k:99d30af3fa91d78cc06cf53a0d4eb2d7fa2a5a72944cc5451311b455a67a3c1c'    },    blockTime: 1705016899793480,    prevBlockHash: 'LbPeMhAF-hLbpG76FO9DJQLtapRtg3ITyHRDpqec1wg',    blockHeight: 2016  },  continuation: null,  txId: null,  preflightWarnings: []}

With this result, you can be confident that your Pact module is protected on the blockchain by the admin-keyset that contains the public key for your administrative account.

Next steps

In this tutorial, you learned how to:

Define a minimal Pact module.
Test a Pact module using the Pact REPL.
Deploy a Pact module on the local development network.
Navigate and view module functions in Chainweaver.
Implement governance for a module using a keyset and using a capability.
Update a deployed module governed by your keyset.

You also verified that other accounts can't make changes to a Pact module governed by your keyset. So far, your election module only contains one simple function that doesn't do very much. The next tutorial demonstrates how to add a schema and a database table to the election module and how to use that table to store the names of election candidates and the number of votes each candidate receives.

You'll also update the list-candidates function to return data from the database table and add a new function to nominate candidates.

To see the code for the activity you completed in this tutorial and get the starter code for the next tutorial, check out the 07-nominate-candidates branch from the election-dapp repository by running the following command in your terminal shell:

bash

git checkout 07-nominate-candidates

bash

git checkout 07-nominate-candidates