In the evolving landscape of blockchain and cryptocurrency, tracking and analyzing data is crucial. One of the most insightful data points for ERC20 tokens is the total supply, which reflects the number of tokens in circulation. The Graph protocol offers an efficient way to query this data through a tool known as a "subgraph". In this article, we will guide you through creating a subgraph that tracks and saves the totalSupply of a specific token (e.g., USDT token on Ethereum - 0xdac17f958d2ee523a2206206994597c13d831ec7) over a million blocks.

Getting started with subgraph development

Setting up your environment

The first step in creating a subgraph is to set up your development environment. This involves installing the Graph CLI. Open your terminal and execute:

npm install -g @graphprotocol/graph-cli

Initializing your subgraph

Once the Graph CLI is installed, you can initialize your subgraph project with the following command:

graph init --allow-simple-name

Answer the questions from the cli the following way:

✔ Protocol · ethereum
✔ Product for which to initialize · hosted-service
✔ Subgraph name · erc20_historical_total_supply
✔ Directory to create the subgraph in · erc20_historical_total_supply
? Ethereum network … 
✔ Ethereum network · mainnet
✔ Contract address · 0xdac17f958d2ee523a2206206994597c13d831ec7
✔ Fetching ABI from Etherscan
✖ Failed to fetch Start Block: Failed to fetch contract creation transaction hash
  
✔ Start Block · 4634747
✔ Contract Name · Contract
✔ Index contract events as entities (Y/n) · true

The command line utility will create a subgraph template project for you. Here we’ve chosen the start block as a block of the smart contract deployment.

Crafting the subgraph manifest

The heart of your subgraph is the manifest file, named subgraph.yaml. This file defines the data sources and how your subgraph interacts with the blockchain. For tracking an ERC20 token’s totalSupply, your manifest file would be structured as follows:

specVersion: 0.0.5
schema:
  file: ./schema.graphql
dataSources:
  - kind: ethereum
    name: Contract
    network: mainnet
    source:
      address: "0xdac17f958d2ee523a2206206994597c13d831ec7"
      abi: Contract
      startBlock: 17640663
    mapping:
      kind: ethereum/events
      apiVersion: 0.0.7
      language: wasm/assemblyscript
      entities:
        - TotalSupply
      abis:
        - name: Contract
          file: ./abis/Contract.json
      eventHandlers:
        - event: Transfer(indexed address,indexed address,uint256)
          handler: handleTransfer
      file: ./src/contract.ts

Defining the GraphQL schema

Your subgraph will store and query data according to a GraphQL schema. In our case, the schema (schema.graphql) for the total supply might look like this:

type TotalSupply @entity(immutable: true) {
  id: Bytes!
  value: BigInt! 
  blockNumber: BigInt!
}

Implementing the mapping logic

The mapping file (mapping.ts) contains the logic for processing blockchain events. Here’s an example of how you might handle Transfer events to update the total supply:

import { Transfer } from "../generated/Contract/Contract"
import { TotalSupply } from "../generated/schema"
import { BigInt, Address } from "@graphprotocol/graph-ts"
import { Contract } from "../generated/Contract/Contract" 

export function handleTransfer(event: Transfer): void {
  let zeroAddress = Address.fromString("0x0000000000000000000000000000000000000000")
  if (event.params.from.equals(zeroAddress) || event.params.to.equals(zeroAddress)) {
    let totalSupply = new TotalSupply(event.transaction.hash.concatI32(event.logIndex.toI32()))

    let contract = Contract.bind(event.address)
    let totalSupplyResult = contract.try_totalSupply()
    if (!totalSupplyResult.reverted) {
      totalSupply.value = totalSupplyResult.value
      totalSupply.blockNumber = event.block.number
      totalSupply.save()
    }

  }
}

Here we process each Transfer event and filtering by the transfers with zero address as a sender or receiver because these actions are related to mints and burns changing the actual total supply of the token.

Building and deploying your subgraph

After setting up these files, you can build and deploy your subgraph with the following commands.

graph codegen
graph build

graph deploy --node https://api.graph-ams.p2pify.com/940a577dc77637743ce420baed763b62/deploy --ipfs https://api.graph-ams.p2pify.com/940a577dc77637743ce420baed763b62/ipfs erc20_subgraph

Replace <ACCESS_TOKEN> with your access token from Chainstack Subgraphs hosting.
Also before this action you need to add an elastic subgraph via the planform UI.

Querying the subgraph for the token total supply over a range of blocks

Once your subgraph is deployed and running, querying the data it indexes becomes a crucial part of extracting meaningful insights. Specifically, if you're interested in analyzing the totalSupply of a token over a range of blocks, you'll utilize the Graph QL API provided by The Graph Protocol. This section will guide you through the process of querying your subgraph to retrieve totalSupply data across a specified block range.

Understanding the query structure

To query a subgraph, you can choose from either of the following Subgraph query options in the subgraph details page:

Query URL — use this URL to query in the CLI.
GraphQL UI URL — use this URL to query in the GraphQL UI.

GraphQL queries are structured to allow you to request exactly what you need. In the context of our subgraph, we are interested in fetching the totalSupply along with the blockNumber for a range of blocks. The basic structure of such a query would be:

{
  totalSupplies(
    orderBy: blockNumber,
    orderDirection: desc
  ) {
    value
    blockNumber
  }
}

The response of the GraphQL interface will look like

{
  "data": {
    "totalSupplies": [
      {
        "value": "60109970000000",
        "blockNumber": "5747917"
      },
      {
        "value": "60109502104300",
        "blockNumber": "5839244"
      },
      {
        "value": "60109502104300",
        "blockNumber": "5869105"
      },
      {
        "value": "60109502104300",
        "blockNumber": "6125686"
      },
      {
        "value": "60109502104300",
        "blockNumber": "6906187"
      },
      {
        "value": "60109502104300",
        "blockNumber": "6941942"
      }
    ]
  }
}

So that one can see the totalSupplies for each block where it has been changed.

Conclusion

Creating a subgraph with Chainstack Subgraphs is a powerful way to access and analyze blockchain data efficiently. By following the steps outlined in this guide, you can track the total supply of an ERC20 token over a vast number of blocks, unlocking valuable insights into its distribution and circulation. This is just the beginning; the potential applications of subgraphs in blockchain data analysis are vast and varied, limited only by your imagination and the specifics of your project.

Tutorials you may like

This is a tutorials collection that will help you to use your subgraphs to the fullest. Before you start, make sure you learn the basics of Chainstack Subgraphs.