Sample Hydra Project

This is a template Hydra project processing account balances from Kusama. Experiment by modifying schema.graphql and the mappings in the mappings folder, defined in manifest.yml.

0. Prerequisites

• Node v14.x
• Postgres database accepting connections
• Docker (optional) for building images

1. Bootstrap

Run

yarn && yarn bootstrap

and generate the model files as defined in schema.graphql, create the database and run all the necessary migrations in one shot.

NB! Don't use in production, as it will delete all the existing records.

2. Generate Types for events and extrinsics

A separate tool Hydra Typegen can be used for generating Typescript classes for the event handlers (the mappings).
Run

yarn typegen

to run the typegen for events and extrinsics defined in manifest.yml (it fetches the metadata from an RPC endpoint and blockhash defined there).

3. Build Mappings

Mappings is a separated TypeScript module created in the mappings folder. The handlers exported by the module should match the ones defined in manifest.yml in the mappings section. Once the necessary files are generated, build it with

yarn mappings:build

4. Run the Query Node API

Run

yarn query-node:start:dev

This will start the query node, but against an empty database. Still, you can already navigate to localhost:4000/graphql

and some query, e.g.:

query {
  accounts(limit: 5, where: { wallet_eq: "5HKcLj5vuexs9K6jAGdjErKijVFciLQzWBoJtj7cmrqe6GpB" }) {
     id
     balance
     wallet
     historicalBalances {
       balance
       timestamp
     }
  }  
}

5. Run the processor

Run the processor to pull the runtime data from the indexer and run the mappings:

yarn processor:start

The query node is now fully functional. You can subsribe to the state via GraphQL subscriptions:

subscription {
  stateSubscription {
    chainHead # current chain height
    indexerHead # last block the Indexer has indexed
    lastProcessedEvent # last event the processor has processed
  }
}

Choosing the Hydra Indexer

The Hydra Indexer endpoint is set by the environment variable INDEXER_ENDPOINT_URL sourced from .env.

Check the official docs for the list of publicly available Hydra Indexers maintained by Subsquid.

If you don't find your substrate chain, contact us and we will setup an Indexer for your chain.

Self-hosted Hydra Indexer

One can also use a self-hosted Hydra Indexer.

The simplest way to run an indexer locally is to use the docker-compose template docker-compose-indexer-template.yml. The following environment variables must be set in .indexer.env:

• Indexer database connection settings: DB_NAME, DB_HOST, DB_PORT, DB_USER, DB_PASS
• Chain RPC endpoint: WS_PROVIDER_ENDPOINT_URI
• If the Substrate runtime uses non-standard types, type definitions or a bundle type overrides should be provided.

Run

docker compose --env-file .indexer.env -f docker-compose-indexer-template.yml up

Follow the links for more information about the indexer service and indexer-api-gateway.