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Pact Accounts and Transfers

Welcome to this tutorial on Accounts and Transfers with Pact!

This tutorial covers the following topics

  • Project Environment Setup
  • Module and Keysets
  • Define Schema and Table
  • Functions
  • Create Table
  • Create Accounts
  • Make Payments
  • Deploy Smart Contract

The goal of this tutorial is to help you build an application that transfers value between two accounts. To do this, you’ll build a smart contract that implements this functionality named Simple Payments. This is an important function of smart contracts and will set you up to create more complex applications using accounts and transfers.

Key Takeaway

Accounts and transfers are a key feature of many smart contracts. Using Pact, you can define tables that track account keysets and values, allowing you to set and update these values as needed.


Pact Accounts and Transfers

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Project Overview

To get started with this application, take a look at the visual overview. This provides a summary of each of the features you will be creating for the simple payment smart contract.

1-project-overview

As you can see, you will create a payments module including 3 functions; create-account, get-balance, and pay. These functions will store data on a payments-table which manages payments between 2 accounts Sarah and James.

Now that you have a basic understanding of the requirements, you can start building the project for yourself!


Project Environment Setup

To get started, choose a project directory and clone the project resources into your local environment.

git clone https://github.com/kadena-io/pact-lang.org-code.git

Change into the loans directory to begin working on this project.

cd pact-lang.org-code/payments

Open this directory in atom to see each of the files provided.

atom .

As you’ll see, there are a few separate folders available to you.

start Provides a starting point with all comments for every challenge.
challenges Challenges in the demo are broken out into separate files, allowing you to build your application over time while having the flexibility to experiment with your own ideas.
finish Includes all comments and code for the final application.
loans Includes final application without the challenge comments.

Each of these options are meant to help support you as you work through these challenges. Feel free to use them however you’d like to.


1. Module and Keyset

The first step is to set up the module and keysets for the smart contract.

Code Challenge

Define and read the admin-keyset, create the payments module, and give the admin-keyset access to the module.

Note

If you’re unfamiliar with modules and keyset, our Pact Modules Tutorial is a great place to get started.


2. Define Schema and Table

The next step is to define the schema and table for the smart contract.

The payments-table, will keep track of the balance of the accounts and associate that to the account’s keyset.

Payments Table

fieldname fieldtype
balance decimal
keyset keyset

Code Challenge

Define a schema and table with columns balance and keyset.

Note

Schema definitions are introduced in the Pact Schemas and Tables Tutorial.


3. Functions

This smart contract will contain 3 functions create-account, get-balance, and pay. Each of these are essential functions to allow users to manage their accounts.

Note

You can review each of the function types in the Schemas and Tables Tutorial as well as the Pact Language Basics Tutorial.

3.1 Create Account

First, add a function that allows the administrator to create accounts. This will allow you to add as many accounts as you’d like.

Code Challenge

Create a function create-account that allows administrator to create accounts.

Note

Try using enforce to regulate who has access to create an account.

3.2 Get Balance

Now that you can create accounts, it is helpful to be able to view the balance of these accounts. In this case, we’ll allow both users and administrators to view the balance.

Code Challenge

Create a function get-balance that allows administrators and users to view the balance of their account.

3.3 Pay

Next, you’ll create the function that allows one account to pay another account. This allows accounts to transfer value from their account to another to begin making payments and managing their finances.

Code Challenge

Create a function pay that allows an account to pay another account.


4. Create Table

You have now completed the module. Outside of the module you can create the table that you defined earlier.

Code Challenge

Create the payments-table.

Note

At this point you have completed the module. You will notice the previous challenge containing a final parenthesis to close out the module. The remaining steps are meant to help you call functions from within the module you created to put your smart contract to use.


5. Create Accounts

The next step is to create the accounts that will transfer value.

For this tutorial, create 2 accounts. Sarah James

To do this, you use the create-account function built earlier. This function takes 3 arguments; id, initial-balance, and keyset.

Code Challenge

Call the create-account function to create accounts for Sarah and James.


6. Make Payment

The final step is to make a payment from one account to another. You can do this using the pay function created earlier.

Code Challenge

Use the pay function to transfer 25.0 to James from Sarah’s account. After making the payment, read the balance of both Sarah and James.


Deploy the Smart Contract

Congratulations, at this point you have completed the Simple Payment smart contract!

If you’d like, you can try deploying this smart contract. You can deploy this contract using the Pact Online Editor or from the Pact Atom SDK. If you choose to deploy this locally, you’ll need the REPL file which you can find inside of the repository you cloned.

For help getting started and deploying in each of these environments, try the following tutorials.


Review

Congratulations on completing the Accounts and Transfers Tutorial!

In this tutorial, you built a Simple Payment application that creates accounts, views account balances, and makes payments between accounts. This is an important function of smart contracts and will set you up to create more complex applications using accounts and transfers.

This is a key feature of many smart contracts and can be extended into all types of use cases. Take some time now to experiment with these features to try them out in creative new ways.