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description
A tool for generating type-safe TypeScript classes for runtime events and extrinsic calls

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({
  event
}: EventContext & StoreContext ) {
  const [from, to, value] = new Balances.TransferEvent(event).params
  const { dest, value } = new Balances.TransferCall(event).args
  ...
}

Quickstart

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

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

It is also possible to run hydra-typegen against a YAML config file

hydra-typegen typegen typegen.yml --debug

Typegen config

Typegen config file has the following structure:

Field Type Description
metadata.source string Where typegen will source node metadata. Can either be a ws endpoint or a path to a static json file with the same content as the result of state_getMetadata RPC call
metadata.blockHash string (optional) If metadata.source is a WS endpoint, hash of the block from which metadata will be sourced, in hex format
events [string] A list of events for which TS classes will be generated, in the format <section>.<name>
calls [string] A list of extrinsics (calls) for which TS classes will be generated, in the format <section>.<method>
outDir string Root directory for the generated classes
strict boolean

Default: false

If true, the event/extrinsic constructor throws an error if the raw data does not match the format in metadata (e.g. due to a runtime upgrade).
customTypes.lib string (optional) Import path for custom types that will be used in the generated sources
customTypes.typedefs string (optional) Path to a JSON file with custom type definitions, as expected by polkadot.js createApi method

The config file typegen.yml can look like this:

# Typegen will pull the metadata from Kusama at block with the given hash
metadata:
  source: wss://kusama-rpc.polkadot.io
  blockHash: '0x45eb7ddd324361adadd4f8cfafadbfb7e0a26393a70a70e5bee6204fc46af62e'
# events and calls for which the typescript types will be generated
events:
  - Balances.Transfer
calls:
  - Balances.transfer
outDir: ./generated

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.

In the config file, place the definition into the customTypes section. It assumes that all the custom runtime types are already available for import from a library, so that e.g. the generated import statement

import { MyCustomRuntimeClass } from 'my/types/library'

is correctly resolved.

...
customTypes:
    lib: 'my/types/library',
    typedefsLoc: my-types-json,

Commands

hydra-typegen typegen [CONFIG]

Generate Typescript classes for the Substrate events

USAGE
  $ hydra-typegen typegen [CONFIG]

ARGUMENTS
  CONFIG  Path to YML config file. Overrides the flag options

OPTIONS
  -c, --calls=calls          Comma-separated list of substrate calls in the format <module>.<name>
  -d, --debug                Output debug info
  -e, --events=events        Comma-separated list of substrate events in the formation <module>.<name>

  -h, --blockHash=blockHash  Hash of the block from which the metadata will be fetched. Only applied if metadata is
                             pulled via an RPC call

  -i, --typelib=typelib      A JavaScript module from which the custom types should be imported, e.g.
                             '@joystream/types/augment'

  -m, --metadata=metadata    [default: metadata.json] Chain metadata source. If starts with ws:// or wss:// the metadata
                             is pulled by an RPC call to the provided endpoint. Otherwise a relative path to a json file
                             matching the RPC call response is expected

  -o, --outDir=outDir        [default: generated/types] A relative path the root folder where the generated files will
                             be generated

  -s, --[no-]strict          Strict mode. If on, the generated code throws an error if the input event argument types
                             don't much the metadata definiton

  -t, --typedefs=typedefs    A relative path to a file with JSON definitions for custom types used by the chain