Terra 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.yaml under the mapping handlers.

There are different classes of mappings functions for Terra; Block handlers, Event Handlers, Transaction Handlers, and Message 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 { TerraBlock } from "@subql/types-terra";

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

A TerraBlock is an extended interface type of Terra.js BlockInfo, but also encapsulates the BlockInfo and TxInfo of all transactions in the block.

Event Handler

You can use event handlers to capture information when certain events are included on a new block. The events that are part of the default runtime and a block may contain multiple events.

During the processing, the event handler will receive an event as an argument with the event'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 { TerraEvent } from "@subql/types-terra";
import { MsgExecuteContract } from "@terra-money/terra.js";

export async function handleEvent(
  event: TerraEvent<MsgExecuteContract>
): Promise<void> {
  const record = new EventEntity(
    `${event.tx.tx.txhash}-${event.msg.idx}-${event.idx}`
  );
  record.blockHeight = BigInt(event.block.block.block.header.height);
  record.txHash = event.tx.tx.txhash;
  await record.save();
}

A TerraEvent encapsulates Event data and TxLog corresponding to the event. It also contains TerraMessage data of the message connected to the event. Also, it includes the TerraBlock and TerraTransaction data of the block and transaction from which the event was emitted.

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 { TerraTransaction } from "@subql/types-terra";

export async function handleTransaction(tx: TerraTransaction): Promise<void> {
  const record = new TransactionEntity(tx.tx.txhash);
  record.blockHeight = BigInt(tx.block.block.block.header.height);
  record.timestamp = tx.tx.timestamp;
  await record.save();
}

The TerraTransaction encapsulates TxInfo and the corresponding TerraBlock in which the transaction occured.

Message Handler

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

import { TerraMessage } from "@subql/types-terra";
import { MsgExecuteContract } from "@terra-money/terra.js";

export async function handleMessage(
  msg: TerraMessage<MsgExecuteContract>
): Promise<void> {
  const record = new MessageEntity(`${msg.tx.tx.txhash}-${msg.idx}`);
  record.blockHeight = BigInt(msg.block.block.header.height);
  record.txHash = msg.tx.txhash;
  record.contract = msg.msg.toData().contract;
  record.sender = msg.msg.toData().sender;
  record.executeMsg = JSON.stringify(msg.msg.toData().execute_msg);
  await record.save();
}

TerraMessage encapsulates the msg object containing the message data, the TerraTransaction in which the message occured in and also the TerraBlock in which the transaction occured in.

Third-party Library Support - the Sandbox

SubQuery is deterministic by design, that means that each SubQuery project is guaranteed to index the same data set. This is a critical factor that is required to decentralise SubQuery in the SubQuery Network. This limitation means that in default configuration, the indexer is by default run in a strict virtual machine, with access to a strict number of third party libraries.

You can easily bypass this limitation however, allowing you to retrieve data from external API endpoints, non historical RPC calls, and import your own external libraries into your projects. In order to do to, you must run your project in unsafe mode, you can read more about this in the references. An easy way to do this while developing (and running in Docker) is to add the following line to your docker-compose.yml:

subquery-node:
  image: onfinality/subql-node:latest
  ...
  command:
    - -f=/app
    - --db-schema=app
    - --unsafe
  ...

When run in unsafe mode, you can import any custom libraries into your project and make external API calls using tools like node-fetch. A simple example is given below:

import { SubstrateEvent } from "@subql/types";
import fetch from "node-fetch";

export async function handleEvent(event: SubstrateEvent): Promise<void> {
  const httpData = await fetch("https://api.github.com/users/github");
  logger.info(`httpData: ${JSON.stringify(httpData.body)}`);
  // Do something with this data
}

By default (when in safe mode), the VM2 sandbox only allows the following:

• only some certain built-in modules, e.g. assert, buffer, crypto,util and path
• third-party libraries written by CommonJS.
• Note HTTP and WebSocket connections are forbidden

Modules and Libraries

To improve SubQuery's data processing capabilities, we have allowed some of the NodeJS's built-in modules for running mapping functions in the sandbox, and have allowed users to call third-party libraries.

Please note this is an experimental feature and you may encounter bugs or issues that may negatively impact your mapping functions. Please report any bugs you find by creating an issue in GitHub.

Built-in modules

Currently, we allow the following NodeJS modules: assert, buffer, crypto, util, and path.

Rather than importing the whole module, we recommend only importing the required method(s) that you need. Some methods in these modules may have dependencies that are unsupported and will fail on import.

import { hashMessage } from "ethers/lib/utils"; // Good way
import { utils } from "ethers"; // Bad way