Moonbeam (EVM) Quick Start

SubQuery TeamAbout 4 min

Moonbeam (EVM) Quick Start

This quick start guide introduces SubQuery's Substrate EVM support by using an example project in Moonbeam Network. The example project indexes all Transfers from the Moonbeam EVM FRAX ERC-20 contract, as well as Collators joining and leaving events from Moonbeam's Staking functions.

This project is unique, as it indexes data from both Moonbeam's Substrate execution layer (native Moonbeam pallets and runtime), with smart contract data from Moonbeam's EVM smart contract layer, within the same SubQuery project and into the same dataset. A very similar approach was taken with indexing Astar's WASM layer too.

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.

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.

The Moonbeam-evm-substrate-starter project has two entities. An Erc20Transfer and Collator. These two entities index ERC-20 transfers related to the $FRAX contract, as well as any collators joining or leaving the Moonbeam Parachain.

type Erc20Transfer @entity {
  id: ID! #id is a required field
  from: String!
  to: String!
  contractAddress: String!
  amount: BigInt!
}

type Collator @entity {
  id: ID! #collator address
  joinedDate: Date!
}

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.

You will find the generated models in the /src/types/models directory.

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.

The Project Manifest File

The Project Manifest (project.ts) file works as an entry point to your project. It defines most of the details on how SubQuery will index and transform the chain data. For Substrate/Polkadot chains, there are three types of mapping handlers:

BlockHanders: On each and every block, run a mapping function
EventHandlers: On each and every Event that matches optional filter criteria, run a mapping function
CallHanders: On each and every extrinsic call that matches optional filter criteria, run a mapping function

For EVM and WASM data processors on Substrate/Polkadot chains, there are only two types of mapping handlers:

EventHandlers: On each and every Event that matches optional filter criteria, run a mapping function
CallHanders: On each and every extrinsic call that matches optional filter criteria, run a mapping function

Substrate Manifest section

Since we are planning to index all Polkadot transfers, we need to update the datasources section as follows:

{
  dataSources: [
    {
      kind: SubstrateDatasourceKind.Runtime,
      startBlock: 1,
      mapping: {
        file: './dist/index.js',
        handlers: [
          {
            handler: 'handleCollatorJoined',
            kind: SubstrateHandlerKind.Call,
            filter: {
              module: 'staking',
              method: 'joinCandidates'
            }
          },
          {
            handler: 'handleCollatorLeft',
            kind: SubstrateHandlerKind.Call,
            filter: {
              module: 'staking',
              method: 'executeLeaveCandidates'
            }
          }
        ]
      }
    },
  ],
}

This indicates that you will be running a handleCollatorJoined mapping function whenever the method joinCandidates is called on the staking pallet. Similarly, we will run handleCollatorLeft whenever the method executeLeaveCandidates is called on the staking pallet. This covers the most basic actions that Collators can do (requesting to join the candidates pool & leaving the candidates pool). For more information about other methods possible under the pallet stakingin Moonbeam, the Moonbeam documentation provides a list of possible functions to call.

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

EVM Manifest Section

If you're not using the EVM-Substrate starter template then please add the frontier EVM Datasource as a dependency using yarn add @subql/frontier-evm-processor.

We are indexing all transfers and approve contract call events from the $FRAX contract 0x322E86852e492a7Ee17f28a78c663da38FB33bfb. First, you will need to import the contract ABI defintion. You can copy the entire JSON and save it as a file ./erc20.abi.json in the root directory.

This section in the Project Manifest now imports all the correct definitions and lists the triggers that we look for on the blockchain when indexing. We add another section the datasource beneath the above substrate manifest section.

{
  dataSources: [
    {
      kind: 'substrate/FrontierEvm',
      startBlock: 189831,
      processor: {
        file: './node_modules/@subql/frontier-evm-processor/dist/bundle.js',
        options: {
          abi: 'erc20',
          // Contract address of $FRAX
          address: '0x322E86852e492a7Ee17f28a78c663da38FB33bfb'
        }
      },
      assets: new Map([['erc20', { file: './erc20.abi.json' }]]),
      mapping: {
        file: './dist/index.js',
        handlers: [
          {
            handler: 'handleErc20Transfer',
            kind: 'substrate/FrontierEvmEvent',
            filter: {
              topics: [
                'Transfer(address indexed from,address indexed to,uint256 value)'
              ]
            }
          },
        ]
      },
    },
  ],
}

The above code indicates that you will be running a handleErc20Transfer mapping function whenever there is an Transfer event on any transaction from the Moonbeam $FRAX contract.

Check out our Substrate EVM documentation to get more information about the Project Manifest (project.ts) file for Substrate EVM contracts.

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. There are the exported functions handleCollatorJoined, handleCollatorLeft and handleErc20Transfer.

export async function handleCollatorJoined(
  call: SubstrateExtrinsic,
): Promise<void> {
  //We added a logger to the top of this function, in order to see the block number of the event we are processing.
  logger.info(`Processing SubstrateEvent at ${call.block.block.header.number}`);

  const address = call.extrinsic.signer.toString();

  const collator = Collator.create({
    id: address,
    joinedDate: call.block.timestamp,
  });

  await collator.save();
}

export async function handleCollatorLeft(
  call: SubstrateExtrinsic,
): Promise<void> {
  //We added a logger to the top of this function, in order to see the block number of the event we are processing.
  logger.info(`Processing SubstrateCall at ${call.block.block.header.number}`);

  const address = call.extrinsic.signer.toString();
  await Collator.remove(address);
}

The handleCollatorJoined and handleCollatorLeft functions receives Substrate event/call data from the native Substrate environment whenever an event/call matches the filters that were specified previously in the project.ts. It extracts the various data from the event/call payload, then checks if an existing Collator record exists. If none exists (e.g. it's a new collator), then it instantiates a new one and then updates the total stake to reflect the new collators. Then the .save() function is used to save the new/updated entity (SubQuery will automatically save this to the database).

export async function erc20Transfer(
  event: MoonbeamEvent<
    [string, string, BigNumber] & { from: string; to: string; value: BigNumber }
  >,
): Promise<void> {
  //We added a logger to the top of this function, in order to see the block number of the event we are processing.
  logger.info(`Processing MoonbeamEvent at ${event.blockNumber.toString()}`);
  const transfer = Erc20Transfer.create({
    id: event.transactionHash,
    from: event.args.from,
    to: event.args.to,
    amount: event.args.value.toBigInt(),
    contractAddress: event.address,
  });

  await transfer.save();
}

The handleErc20Transfer function receives event data from the EVM execution environment whenever an event matches the filters that was specified previously in the project.ts. It instantiates a new Transfer entity and populates the fields with data from the EVM Call payload. Then the .save() function is used to save the new entity (SubQuery will automatically save this to the database).

Check out our mappings documentation for Substrate and the Substrate Frontier EVM data processor to get detailed information on mapping functions for each type.

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.

query {
  erc20Transfers(first: 3, orderBy: BLOCK_HEIGHT_ASC) {
    nodes {
      id
      from
      to
      contractAddress
      amount
    }
  }
}

Tips

There is a Docs tab on the right side of the playground which should open a documentation drawer. This documentation is automatically generated and helps you find what entities and methods you can query. To learn more about the GraphQL Query language here.

You should see results similar to below:

{
  "data": {
    "erc20Transfers": {
      "nodes": [
        {
          "id": "0x6eadc6336e57c95012a0b3fe0bbfdfe4b05870db45f54022f6f0fae99094389e",
          "from": "0xB213A825552FBC78DcA987824F74c8a870696ede",
          "to": "0xd3bE0E32147ae91378F035fF96f3e2cAb96aC48b",
          "contractAddress": "0x322e86852e492a7ee17f28a78c663da38fb33bfb",
          "amount": "421311117864349454574"
        },
        {
          "id": "0x042e355370899571f0a8828e943ac794554b48c3d042a0a26cfd64e3b1107de5",
          "from": "0xd3bE0E32147ae91378F035fF96f3e2cAb96aC48b",
          "to": "0x1d3286A3348Fa99852d147C57A79045B41c4f713",
          "contractAddress": "0x322e86852e492a7ee17f28a78c663da38fb33bfb",
          "amount": "180233014368657600639"
        },
        {
          "id": "0x1fcc93ee0879ade7df0bfbaaaff32b0aef31698865ede29290b5616b59683f5e",
          "from": "0x5f68e72bF781d3927a59Ff74030b87A0F628EB91",
          "to": "0x054Fb7D6c1E3d7771B128Eb6FA63864745284Fc5",
          "contractAddress": "0x322e86852e492a7ee17f28a78c663da38fb33bfb",
          "amount": "24614491694707430571"
        },
        {
          "id": "0x50eecab0be3c46ff1d1aa8effcd1166bbdcb9f28582c2a5f53fd35b25b8cd021",
          "from": "0x2974A0D3e70FDe22d44c188F770beE964205aCad",
          "to": "0xa7A3Cb7d3f9Cf963012fdd54E6de3562A3A5f140",
          "contractAddress": "0x322e86852e492a7ee17f28a78c663da38fb33bfb",
          "amount": "380739794849478795472"
        }
      ]
    }
  }
}

Congratulations! You have now a locally running SubQuery project that accepts GraphQL API requests for transfer events from the $FRAX smart contract at 0x322E86852e492a7Ee17f28a78c663da38FB33bfb.

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.