Hydra Typegen

Motivation

Hydra Typegen is a code generation tool for creating Typescript types for substrate events and extrinsics. Its primary use-case is to provide type-safe interfaces for Hydra mappings. For example, once a typescript class for the Balances.Transfer event is generated, a mapping can look like

export async function balancesTransfer(
  db: DatabaseManager,
  _event: SubstrateEvent
) {
  const event = new Balances.TransferEvent(_event);
  const transfer = new Transfer()
  transfer.from = Buffer.from(event.data.accountIds[0].toHex())
  transfer.to = Buffer.from(event.data.accountIds[1].toHex())
  transfer.value = event.data.balance.toBn()
  transfer.block = event.ctx.blockNumber
  transfer.comment = `Transferred ${transfer.value} from ${transfer.from} to ${transfer.to}`

  console.log(`Saving ${JSON.stringify(transfer, null, 2)}`)

  await db.save<Transfer>(transfer)
}

A full sample Hydra project can be found here

Usage

For usage and a list of supported flags, type

hydra-typegen typegen --help

A minimal example for generating classes for the Balances.Transfer and Treasury.Deposit events in Kusama:

hydra-typegen --metadata wss://kusama-rpc.polkadot.io Balances.Transfer,Treasury.Deposit

Custom types

Hydra Typegen supports custom substrate types via the --typedefs flag. The provided .json file should include type definitions for the arguments and parameters of the events and extrinsics to be generated. The type definitions file is copied to the generated sources.