Gnosis Mapping

Important

We use Ethereum types (e.g. EthereumBlock, EthereumTransaction, and EthereumLog) for Gnosis. Since Gnosis is a layer-2 scaling solution, we can use the core Ethereum framework to index it.

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

• Mappings are defined in the src/mappings directory and are exported as a function.
• These mappings are also exported in src/index.ts.
• The mappings files are reference in project.ts under the mapping handlers.
• The mappings are run from within a Sandbox

There are different classes of mappings functions for Gnosis; Block handlers, Transaction Handlers, and Log Handlers.

Block Handler

You can use block handlers to capture information each time a new block is attached to the chain, e.g. block number. To achieve this, a defined BlockHandler will be called once for every block.

Using block handlers slows your project down as they can be executed with each and every block - only use if you need to.

import { EthereumBlock } from "@subql/types-ethereum"; // We use ethereum types since Gnosis is a layer-2 that is compatible

export async function handleBlock(block: EtheruemBlock): Promise<void> {
  // Create a new BlockEntity with the block hash as it's ID
  const record = new BlockEntity(block.blockHash);
  record.height = BigInt(block.blockNumber);
  await record.save();
}

Transaction Handler

You can use transaction handlers to capture information about each of the transactions in a block. To achieve this, a defined TransactionHandler will be called once for every transaction. You should use Mapping Filters in your manifest to filter transactions to reduce the time it takes to index data and improve mapping performance.

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

export async function handleTransaction(tx: ApproveTransaction): Promise<void> {
  logger.info(`New Approval transaction at block ${tx.blockNumber}`);
  const approvalRecord = Approval.create({
    id: tx.hash,
    owner: tx.from,
    spender: await tx.args[0],
    value: BigInt(await tx.args[1].toString()),
    contractAddress: tx.to,
  });

  await approvalRecord.save();
}

Log Handler

You can use log handlers to capture information when certain logs are included on transactions. During the processing, the log handler will receive a log as an argument with the log's typed inputs and outputs. Any type of event will trigger the mapping, allowing activity with the data source to be captured. You should use Mapping Filters in your manifest to filter events to reduce the time it takes to index data and improve mapping performance.

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

export async function handleLog(log: TransferLog): Promise<void> {
  logger.info(`New transfer transaction log at block ${log.blockNumber}`);
  const transferRecord = Transfer.create({
    id: log.transactionHash,
    value: log.args.value.toBigInt(),
    from: log.args.from,
    to: log.args.to,
    contractAddress: log.address,
  });

  await transferRecord.save();
}

Querying Contracts

We globally provide an api object that implements an Ethers.js Provider. This will allow querying contract state at the current block height being indexed. The easiest way to use the api is with Typechain, with this you can generate typescript interfaces that are compatible with this api that make it much easier to query your contracts.

You can then query contract state at the right block height. For example to query the token balance of a user at the current indexed block height (please note the two underscores in Erc20__factory):

// Create an instance of the contract, you can get the contract address from the Transaction or Log
// Note the two underscores __ in `Erc20__factory`
const erc20 = Erc20__factory.connect(contractAddress, api);

// Query the balance of an address
const balance = await erc20.balanceOf(address);

The above example assumes that the user has an ABI file named erc20.json, so that TypeChain generates ERC20__factory class for them. Check out this example to see how to generate factory code around your contract ABI using TypeChain.