Polygon zkEVM Quick Start

SubQuery TeamAbout 3 min

Polygon zkEVM Quick Start

The goal of this quick start guide is to index all transfers and approval events from the Wrapped Eth on Polygon zkEVM Network .

Please initialise an a Polygon zkEVM project.

In the earlier Quickstart section , you should have taken note of three crucial files. To initiate the setup of a project from scratch, you can proceed to follow the steps outlined in the initialisation description.

As a prerequisite, you will need to generate types from the ABI files of each smart contract. Additionally, you can kickstart your project by using the EVM Scaffolding approach (detailed here). You'll find all the relevant events to be scaffolded in the documentation for each type of smart contract.

Note

The final code of this project can be found here.

We use Ethereum packages, runtimes, and handlers (e.g. @subql/node-ethereum, ethereum/Runtime, and ethereum/*Hander) for Polygon zkEVM. Since Polygon zkEVM is an EVM-compatible layer-2 scaling solution, we can use the core Ethereum framework to index it.

Your Project Manifest File

The Project Manifest file is an entry point to your project. It defines most of the details on how SubQuery will index and transform the chain data.

For EVM chains, there are three types of mapping handlers (and you can have more than one in each project):

BlockHanders: On each and every block, run a mapping function
TransactionHandlers: On each and every transaction that matches optional filter criteria, run a mapping function
LogHanders: On each and every log that matches optional filter criteria, run a mapping function

As we are indexing all transfers and approvals from the Wrapped ETH contract on Polygon zkEVM network, the first step is to import the contract abi definition which can be obtained from from any standard ERC-20 contract. Copy the entire contract ABI and save it as a file called erc20.abi.json in the /abis directory.

Update the datasources section as follows:

{
  dataSources: [
    {
      kind: EthereumDatasourceKind.Runtime,
      startBlock: 1, // This is the block that the contract was deployed on https://zkevm.polygonscan.com/token/0x4f9a0e7fd2bf6067db6994cf12e4495df938e6e9
      options: {
        // Must be a key of assets
        abi: "erc20",
        // This is the contract address for Wrapped Ether https://zkevm.polygonscan.com/token/0x4f9a0e7fd2bf6067db6994cf12e4495df938e6e9
        address: "0x4f9a0e7fd2bf6067db6994cf12e4495df938e6e9",
      },
      assets: new Map([["erc20", { file: "./abis/erc20.abi.json" }]]),
      mapping: {
        file: "./dist/index.js",
        handlers: [
          {
            kind: EthereumHandlerKind.Call,
            handler: "handleTransaction",
            filter: {
              /**
               * The function can either be the function fragment or signature
               * function: '0x095ea7b3'
               * function: '0x7ff36ab500000000000000000000000000000000000000000000000000000000'
               */
              function: "approve(address spender, uint256 rawAmount)",
            },
          },
          {
            kind: EthereumHandlerKind.Event,
            handler: "handleLog",
            filter: {
              /**
               * Follows standard log filters https://docs.ethers.io/v5/concepts/events/
               * address: "0x60781C2586D68229fde47564546784ab3fACA982"
               */
              topics: [
                "Transfer(address indexed from, address indexed to, uint256 amount)",
              ],
            },
          },
        ],
      },
    },
  ],
}

The above code indicates that you will be running a handleTransaction mapping function whenever there is a approve method being called on any transaction from the WETH contract.

The code also indicates that you will be running a handleLog mapping function whenever there is a Transfer event being emitted from the WETH contract.

Check out our Manifest File documentation to get more information about the Project Manifest (project.ts) file.

Update Your GraphQL Schema File

The schema.graphql file determines the shape of your data from SubQuery due to the mechanism of the GraphQL query language. Hence, updating the GraphQL Schema file is the perfect place to start. It allows you to define your end goal right at the start.

Remove all existing entities and update the schema.graphql file as follows. Here you can see we are indexing block information such as the id, blockHeight, transfer receiver and transfer sender along with an approvals and all of the attributes related to them (such as owner and spender etc.).

type Transfer @entity {
  id: ID! # Transaction hash
  blockHeight: BigInt
  to: String!
  from: String!
  value: BigInt!
  contractAddress: String!
}

type Approval @entity {
  id: ID! # Transaction hash
  blockHeight: BigInt
  owner: String!
  spender: String!
  value: BigInt!
  contractAddress: String!
}

Note

Importantly, these relationships can not only establish one-to-many connections but also extend to include many-to-many associations. To delve deeper into entity relationships, you can refer to this section. If you prefer a more example-based approach, our dedicated Hero Course Module can provide further insights.

SubQuery simplifies and ensures type-safety when working with GraphQL entities, smart contracts, events, transactions, and logs. The SubQuery CLI will generate types based on your project's GraphQL schema and any contract ABIs included in the data sources.

yarn

yarn codegen

npm

npm run-script codegen

This action will generate a new directory (or update the existing one) named src/types. Inside this directory, you will find automatically generated entity classes corresponding to each type defined in your schema.graphql. These classes facilitate type-safe operations for loading, reading, and writing entity fields. You can learn more about this process in the GraphQL Schema section.

It will also generate a class for every contract event, offering convenient access to event parameters, as well as information about the block and transaction from which the event originated. You can find detailed information on how this is achieved in the EVM Codegen from ABIs section. All of these types are stored in the src/types/abi-interfaces and src/types/contracts directories.

You can conveniently import all these types:

import { Approval, Transfer } from "../types";
import {
  ApproveTransaction,
  TransferLog,
} from "../types/abi-interfaces/Erc20Abi";

Check out the GraphQL Schema documentation to get in-depth information on schema.graphql file.

Now that you have made essential changes to the GraphQL Schema file, let’s proceed ahead with the Mapping Function’s configuration.

Add a Mapping Function

Mapping functions define how blockchain data is transformed into the optimised GraphQL entities that we previously defined in the schema.graphql file.

Navigate to the default mapping function in the src/mappings directory. You will be able to see two exported functions handleLog and handleTransaction:

import { Approval, Transfer } from "../types";
import {
  ApproveTransaction,
  TransferLog,
} from "../types/abi-interfaces/Erc20Abi";
import assert from "assert";

export async function handleLog(log: TransferLog): Promise<void> {
  logger.info(`New transfer transaction log at block ${log.blockNumber}`);
  assert(log.args, "No log.args");

  const transaction = Transfer.create({
    id: log.transactionHash,
    blockHeight: BigInt(log.blockNumber),
    to: log.args.to,
    from: log.args.from,
    value: log.args.value.toBigInt(),
    contractAddress: log.address,
  });

  await transaction.save();
}

export async function handleTransaction(tx: ApproveTransaction): Promise<void> {
  logger.info(`New Approval transaction at block ${tx.blockNumber}`);
  assert(tx.args, "No tx.args");

  const approval = Approval.create({
    id: tx.hash,
    owner: tx.from,
    spender: await tx.args[0],
    value: BigInt(await tx.args[1].toString()),
    contractAddress: tx.to,
  });

  await approval.save();
}

The handleLog function receives a log parameter of type TransferLog which includes log data in the payload. We extract this data and then save this to the store using the .save() function (Note that SubQuery will automatically save this to the database).

The handleTransaction function receives a tx parameter of type ApproveTransaction which includes transaction data in the payload. We extract this data and then save this to the store using the .save() function (Note that SubQuery will automatically save this to the database).

Note

For more information on mapping functions, please refer to our Mappings documentation.

Build Your Project

Next, build your work to run your new SubQuery project. Run the build command from the project's root directory as given here:

yarn

yarn build

npm

npm run-script build

Important

Whenever you make changes to your mapping functions, you must rebuild your project.

Now, you are ready to run your first SubQuery project. Let’s check out the process of running your project in detail.

Whenever you create a new SubQuery Project, first, you must run it locally on your computer and test it and using Docker is the easiest and quickiest way to do this.

Run Your Project Locally with Docker

The docker-compose.yml file defines all the configurations that control how a SubQuery node runs. For a new project, which you have just initialised, you won't need to change anything.

However, visit the Running SubQuery Locally to get more information on the file and the settings.

Run the following command under the project directory:

yarn

yarn start:docker

npm

npm run-script start:docker

Note

It may take a few minutes to download the required images and start the various nodes and Postgres databases.

Query your Project

Next, let's query our project. Follow these three simple steps to query your SubQuery project:

Open your browser and head to http://localhost:3000.
You will see a GraphQL playground in the browser and the schemas which are ready to query.
Find the Docs tab on the right side of the playground which should open a documentation drawer. This documentation is automatically generated and it helps you find what entities and methods you can query.

Try the following queries to understand how it works for your new SubQuery starter project. Don’t forget to learn more about the GraphQL Query language.

# Write your query or mutation here
{
  query {
    transfers(first: 5, orderBy: VALUE_DESC) {
      totalCount
      nodes {
        id
        blockHeight
        from
        to
        value
        contractAddress
      }
    }
  }
  approvals(first: 5, orderBy: BLOCK_HEIGHT_DESC) {
    nodes {
      id
      blockHeight
      owner
      spender
      value
      contractAddress
    }
  }
}

You will see the result similar to below:

{
  "data": {
    "query": {
      "transfers": {
        "totalCount": 901,
        "nodes": [
          {
            "id": "0x11c3519a07d48ca7e9b3d77c9c288919e8786dfffaad76bdfd6ae554d2481a13",
            "blockHeight": "3072",
            "from": "0xC6c893a0dCf31b5766Ac5c103AF9e9805A6d0774",
            "to": "0xd8E1E7009802c914b0d39B31Fc1759A865b727B1",
            "value": "4390819482026157205",
            "contractAddress": "0x4F9A0e7FD2Bf6067db6994CF12E4495Df938E6e9"
          },
          {
            "id": "0x8d2eed830280b0e35165560f7234da3ccd02f9dc526434e874ccb0e5a464c4f6",
            "blockHeight": "936",
            "from": "0xd8E1E7009802c914b0d39B31Fc1759A865b727B1",
            "to": "0x267816F8789a28463cE10acD50ffeDDE57F318Ee",
            "value": "3499686336793644484",
            "contractAddress": "0x4F9A0e7FD2Bf6067db6994CF12E4495Df938E6e9"
          },
          {
            "id": "0x818086a329ca6cecfaf55ac6f3c5a34b985a97ef5439c15bb66f094b4e76a8e5",
            "blockHeight": "2841",
            "from": "0xd8E1E7009802c914b0d39B31Fc1759A865b727B1",
            "to": "0xC6c893a0dCf31b5766Ac5c103AF9e9805A6d0774",
            "value": "3300395407835132030",
            "contractAddress": "0x4F9A0e7FD2Bf6067db6994CF12E4495Df938E6e9"
          },
          {
            "id": "0x08e395f3058c05141ab656e08fba91d47d52c9bc954e26f378e4edd3f4ef9d8d",
            "blockHeight": "2435",
            "from": "0x4b8f52c68594554DdF13aff5E2d8d788bC56Ca8c",
            "to": "0xd8E1E7009802c914b0d39B31Fc1759A865b727B1",
            "value": "1794066117854317399",
            "contractAddress": "0x4F9A0e7FD2Bf6067db6994CF12E4495Df938E6e9"
          },
          {
            "id": "0x0ac0c00fd9c3bb4ee921e82fe32e658846497697447d9dadffaaec64b2c5ff4a",
            "blockHeight": "2998",
            "from": "0x7D9195077671B08F442B2A1b310858bDB1C4abcc",
            "to": "0xd8E1E7009802c914b0d39B31Fc1759A865b727B1",
            "value": "1430946047728089377",
            "contractAddress": "0x4F9A0e7FD2Bf6067db6994CF12E4495Df938E6e9"
          }
        ]
      }
    },
    "approvals": {
      "nodes": [
        {
          "id": "0xccec6946012d52a27fcae9790ade5a5e7314f934170483fecf2896e3448604bd",
          "blockHeight": null,
          "owner": "0x12680Ad2f3D80b162344Ba3FF3978daB7A565675",
          "spender": "0xd8E1E7009802c914b0d39B31Fc1759A865b727B1",
          "value": "115792089237316195423570985008687907853269984665640564039457584007913129639935",
          "contractAddress": "0x4F9A0e7FD2Bf6067db6994CF12E4495Df938E6e9"
        }
      ]
    }
  }
}

Note

The final code of this project can be found here.

What's next?

Congratulations! You have now a locally running SubQuery project that accepts GraphQL API requests for transferring data.

Tip

Find out how to build a performant SubQuery project and avoid common mistakes in Project Optimisation.

Click here to learn what should be your next step in your SubQuery journey.