NEAR Mapping

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 NEAR; Block handlers, Transaction Handlers, and Action 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 { NearBlock } from "@subql/types-near";

export async function handleBlock(block: NearBlock): Promise<void> {
  logger.info(`Handling block ${block.header.height}`);

  const blockRecord = NearBlockEntity.create({
    id: block.header.height.toString(),
    hash: block.header.hash,
    author: block.author,
    timestamp: BigInt(block.header.timestamp),
  });

  await blockRecord.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 Transaction Filters in your manifest to filter transactions to reduce the time it takes to index data and improve mapping performance.

import { NearTransaction } from "@subql/types-near";

export async function handleTransaction(
  transaction: NearTransaction,
): Promise<void> {
  logger.info(`Handling transaction at ${transaction.block_height}`);

  const transactionRecord = NearTxEntity.create({
    id: `${transaction.block_hash}-${transaction.result.id}`,
    signer: transaction.signer_id,
    receiver: transaction.receiver_id,
  });

  await transactionRecord.save();
}

The NearTransaction encapsulates transaction info, result, the corresponding block details and the list of NearAction entities that occured in the specific transaction.

Action Handler

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

import { NearAction, Transfer } from "@subql/types-near";

export async function handleAction(
  action: NearAction<Transfer>,
): Promise<void> {
  // An Action can belong to either a transaction or a receipt
  // To check which one, we can check if action.transaction is null
  // If it is null, then it belongs to a receipt
  logger.info(
    `Handling action at ${
      action.transaction
        ? action.transaction.block_height
        : action.receipt.block_height
    }`,
  );

  const id = action.transaction
    ? `${action.transaction.block_height}-${action.transaction.result.id}-${action.id}`
    : `${action.receipt.block_height}-${action.receipt.id}-${action.id}`;
  const sender = action.transaction
    ? action.transaction.signer_id
    : action.receipt.predecessor_id;
  const receiver = action.transaction
    ? action.transaction.receiver_id
    : action.receipt.receiver_id;

  const actionRecord = NearActionEntity.create({
    id: id,
    sender: sender,
    receiver: receiver,
    amount: BigInt((action.action as Transfer).deposit.toString()),
    payloadString: JSON.stringify(action.action.args.toJson()),
  });

  await actionRecord.save();
}

NearAction encapsulates the action object containing the action data and the NearTransaction or NearReceipt in which the action occured in. The payload of the action is stored on the args. In many cases, args are base64 encoded and JSON formatted, in this case you can use action.action.args.toJson(); to decode the arguments.

RPC Calls

We also support some API RPC methods here that are remote calls that allow the mapping function to interact with the actual node and chain state.

Documents in NEAR JsonRpcProvider provide some methods to interact with the NEAR RPC API.