Hedera Graph Indexing Demo

This project demonstrates how to use The Graph to index and query data from a Hedera smart contract deployed on testnet. It includes a simple price feed contract, a subgraph configuration, and TypeScript scripts to interact with both the contract and the indexed data.

As The Graph project (https://thegraph.com/) does not support Hedera yet, you will have to run a local Graph node.

Project Structure

.
├── contracts/             # Smart contract code
│   ├── abi/               # Folder where ABI file is stored
│   └── PriceFeed.sol      # Sample price feed contract
├── scripts/               # TypeScript scripts
│   ├── deploy.ts          # Contract deployment script
│   ├── update.ts          # Script to update prices
│   └── query-history.ts   # Script to query price history
├── subgraph/              # The Graph configuration
│   ├── schema.graphql     # GraphQL schema
│   ├── subgraph.yaml      # Subgraph manifest
│   ├── abis/              # Folder to put ABI fles
│   └── src/               # TypeScript sources
│      └── mapping.ts      # AssemblyScript mappings
├── graph-node/            # Local Graph Node configuration
├── package.json           # Node.js dependencies
└── tsconfig.json          # TypeScript configuration
└── .env.example           # .env file template
└── README.md              # This document

Smart Contract

The sample contract (PriceFeed.sol) implements a simple price feed with events that can be indexed by The Graph. It includes:

• Price update events
• Basic price management functions

Subgraph

The subgraph configuration includes:

• GraphQL schema definition
• Event mappings for price updates
• Contract ABI integration

Scripts

Scripts are supporting:

• Deploying the smart contract on Hedera testnet, and updating the project's configuration
• Interacting with the smart contract to update the price records
• Querying local Graph node to see the price history

Setup

Prerequisites

• Node.js 20+
• Docker and Docker Compose to deploy the local Graph node
• Hedera testnet account
• Solidity compiler installed
• An account on Hedera Testnet (both ECDSA and ED25519 keys work)

Install project dependencies:

pnpm install

Configure your environment:

cp .env.example .env

Edit .env with your credentials:

HEDERA_OPERATOR_ID=[Your Hedera testnet account ID]
HEDERA_OPERATOR_KEY=[Your account's HEX Encoded Private Key]
CONTRACT_ID=[this will be edited after deploying the contract]

Build the contract and generatie ABI file

solc --abi contracts/PriceFeed.sol -o contracts/abi --overwrite
solc --bin contracts/PriceFeed.sol -o contracts --overwrite

Deploy the contract

pnpm run deploy

This will:

• Deploy the contract to Hedera testnet
• Update the subgraph configuration with the new contract address
• Provide the contract ID to be copied to the .env file

Add the deployed contract id to your environment:

Edit .env file:

HEDERA_OPERATOR_ID=[Your Hedera testnet account ID]
HEDERA_OPERATOR_KEY=[Your account's HEX Encoded Private Key]
CONTRACT_ID=[Contract ID provided by deploy.ts in the previous step]

Start the local Graph Node:

First, remove the .keep file from posdtgres data directory, as postgres requires a clean directory to initialize

rm graph-node/data/postgres/.keep

Then run the node

cd graph-node
docker compose up -d
cd ..

You can confirm, that the node is up by looking into docker logs and check indexing status using http://localhost:8030/graphql/playground

Deploy the subgraph

Copy the contract's ABI file:

cp contracts/abi/PriceFeed.abi subgraph/abis/

Deploy the subgraph, when asked for version label to use, enter anything 1 for example.

cd subgraph
npx graph codegen
npx graph build
npx graph create --node http://localhost:8020 hedera-pricefeed-test
npx graph deploy --node http://localhost:8020 --ipfs http://localhost:5001 hedera-pricefeed-test
cd ..

Usage

Update Prices

To update a price for an asset:

pnpm run update -- --price=123456 --asset=BTC

Parameters:

• --price: Price in cents (default: 55000)
• --asset: Asset name (default: "BTC")

⚠️ Note: On Windows passing arguments by node does not work, you will need to run the script directly:

 ts-node scripts/update.ts --price=55000 --asset=BTC

Query Price History

To view the price history and indexing status:

pnpm run query

This will show:

• Current indexing status
• Latest indexed block with timestamp
• Chain head block with timestamp
• Price history grouped by asset

License

MIT