Tutorial

Build a Hydra Indexer and GraphQL server from scratch under five minutes

Before starting, make surehydra-cliis installed on your machine together with all the prerequisites.

0. Hello Hydra!

Start off by setting up a project folder

mkdir hello-hydra && cd hello-hydra

1. From zero to one

Next, run the scaffold command, which generates all the required files:

hydra-cli scaffold

Answer the prompts and the scaffolder will generate a sample backbone for our Hydra project. This includes:

• Sample GraphQL data schema in schema.graphql describing proposals in the Kusama network

• Sample mapping scripts in the ./mapping folder translating substrate events into the Proposal entity CRUD operations

• docker-compose.yml for running a Postgres instance locally as a Docker service.

• .env with all the necessary environment variables.

• package.json with a few utility yarn scripts to be used later on.

2. Codegen

Now all is set for generating the Graphql server and the indexer for Kusama proposals:

hydra-cli codegen

The codegen command creates two separate projects:

• ./generated/graphql-server: this is a GraphQL for querying the proposals

• ./generated/indexer: this is a background indexer tool that fetches the blocks from the Substrate chain (in this case the public Kusama network) and updates the database calling the mapping scripts

3. Set up the database

Now it's time to set up the database:

yarn db:start

This command simply spins up a Postgres Docker image.

yarn db:bootstrap

This creates a DB schema for our data model described in schema.graphql.

4. Start Hydra Indexer

Finally, we're ready to run the indexer and the GraphQL server:

yarn indexer:start

Keep an eye on the output to keep track of the indexer's progress.

5. Start Hydra GraphQL server

In a separate terminal window:

yarn server:start:dev

The last command starts the server in the dev mode and you will see a GraphQL playground opening in your browser (if not, navigate manually to localhost:4000/graphql). It's time to explore all the GraphQL queries supported out-of-the-box! Note, that depending on the starting block it may take a considerable time for the indexer to catch up with the Kusama network, and until then queries may return empty results.

6. Dockerize

Among other things, the scaffolder generates a top-level package.jsonwith a bunch of convenient yarn targets. For example, putting your Hydra Indexer and GraphQL server is easy as running the following targets:

yarn docker:indexer:build

yarn docker:server:build

This will create Docker images named hydra-indexer and hydra-graphql-server

What to do next?

• Explore more examples

• Describe your own schema in schema.graphql

• Write your indexer mappings

• Push your Hydra indexer and GraphQL Docker images to Docker Hub and deploy