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
exportasyncfunctionbalancesTransfer( db:DatabaseManager, _event:SubstrateEvent) {constevent=newBalances.TransferEvent(_event);consttransfer=newTransfer()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.blockNumbertransfer.comment =`Transferred ${transfer.value} from ${transfer.from} to ${transfer.to}`console.log(`Saving ${JSON.stringify(transfer,null,2)}`)awaitdb.save<Transfer>(transfer)}
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
It is also possible to run hydra-typegen against a manifest file:
hydra-typegentypegentypegen.yml--debug
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
Hydra-typegen also supports config files like the one below:
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/definitions
is correctly resolved.
...
customTypes:
lib: <from where the custom types are imported>,
typedefs: <path to a json file with custom runtime types definitions>,