Module 1: Getting started

Introduction

In this module, you will become familiar with SubQuery and get some hands-on experience by creating a simple Hello World SubQuery project. This project will use the subql CLI to create an empty project shell. Then a code will be provided to query the Polkadot mainnet for the blockheight. Note that a Docker environment will be used to simplify the running process.

Reference

• Hello World PDF workbook
• Subql Starter Github

Pre-Requisites

You will require the following:

• NPM package manager.
• SubQuery CLI (@subql/cli).
• Docker.

NPM Package Manager

First, you must check whether you have installed the latest version of node or not.

Run this command:

node -v

It should return a result with the latest version of npm, if you have it installed. For eg:

v18.2.0

Note

Node v12 or higher is required.

If you haven't installed the npm, please run the following command in your terminal and install the latest version of node.

brew update
brew install node
node -v

You will get the latest npm version as the output in the end.

SubQuery CLI

• First, run the following command. It installs the subql cli.

npm install -g @subql/cli

• Then check the subql cli version by running the given below command:

subql -v

You will get an output similar to this: @subql/cli/1.0.1 darwin-x64 node-v18.2.0

Docker

Please visit Docker's official site for instructions on how to install Docker for your specific operating system.

Exercise 1: Hello World

Overview of Steps Involved

1. Initialise a project.
2. Update your mappings.
3. Update your manifest file.
4. Update your graphql schema file.
5. Generate your code.
6. Build your code.
7. Deploy your code in Docker.

Detailed Steps

Step 1: Initialise Your Project

The first step to create a SubQuery project with the following command:

$ subql init
Project name [subql-starter]: HelloWorld
? Select a network family Substrate
? Select a network Polkadot
? Select a template project subql-starter     Starter project for subquery
RPC endpoint: [wss://polkadot.api.onfinality.io/public-ws]:
Git repository [https://github.com/subquery/subql-starter]:
Fetching network genesis hash... done
Author [Ian He & Jay Ji]: Sean
Description [This project can be use as a starting po...]:
Version [1.0.0]:
License [MIT]:
Preparing project... done
HelloWorld is ready

Note that any text in the square brackets are the default values, which will be used if nothing is provided.

This creates a framework and the following directory structure, saving your time.

Step 2: Update the Mappings File

The initialisation command pre-creates a sample mappings file with 3 functions: handleBlock, handleEvent and handleCall. We will focus on the first function called handleBlock for this excerise. Hence, delete the remaining functions.

• The mappingHandler.ts file should look like this:

import {SubstrateExtrinsic,SubstrateEvent,SubstrateBlock} from "@subql/types";
import {StarterEntity} from "../types";
import {Balance} from "@polkadot/types/interfaces";

export async function handleBlock(block: SubstrateBlock): Promise<void> {
    //Create a new starterEntity with ID using block hash
    let record = new StarterEntity(block.block.header.hash.toString());
    //Record block number
    record.field1 = block.block.header.number.toNumber();
    await record.save();
}

Step 3: Update the Manifest File (aka project.yaml)

The initialisation command also pre-creates a sample manifest file and defines 3 handlers. Since you have removed handleEvent and handleCall from the mappings file, you have to remove them from the manifest file as well.

• The updated part of the manifest file should look like this:

dataSources:
  - kind: substrate/Runtime
    startBlock: 1
    mapping:
      file: ./dist/index.js
      handlers:
        - handler: handleBlock
          kind: substrate/BlockHandler

Step 4: Update the Graphql Schema

The default schema.graphql file will contain 5 fields. We can remove the fields from 2 to 5, because the handleBlock function in the mappings file only uses “field1”.

Note

Rename field1 to something more meaningful. Eg blockHeight. Note that if you do this, don’t forget to update the reference to field1 in the mappings file appropriately.

The schema file should look like this:

type StarterEntity @entity {
  id: ID! #id is a required field
  blockHeight: Int!
}

Step 5: Install the Dependencies

Install the node dependencies by running the following commands:

yarn

yarn install

npm

npm install

Step 6: Generate the Associated Typescript

Next, we will generate the associated typescript with the following command:

yarn

yarn codegen

npm

npm run-script codegen

You should see a new folder appear with 2 new files.

Step 7: Build the Project

The next step is to build the project with the following command:

yarn

yarn build

npm

npm run-script build

This bundles the app into static files for production.

Step 8: Start the Docker Container

Run the docker command to pull the images and to start the container.

docker-compose pull && docker-compose up

Important

You need to have Docker installed as noted in the prerequisite.

Step 9: Run a Query

Once the docker container is up and running, which could take a few minutes, open up your browser, and navigate to www.localhost:3000.

This will open up a “playground” where you can create your query. Copy the example below.

{
  query{
    starterEntities(last:10, orderBy: FIELD1_ASC){
      nodes{
        field1
      }
    }
  }
}

Note

If you renamed field1 something else, modify this query appropriately.