Squid template project

A starter Squid project to demonstrate its structure and conventions. It accumulates kusama account balances and serves them via GraphQL API. For a full reference of Subsquid features consult Docs and FAQ.

Summary

• Quickstart
• Setup for Parachains
• Setup for Localnets, Devnets and Testnets
• Development flow
  • Database Schema
  • Entity classes
  • DB migrations
  • Typegen for Events, Extrinsics and Storage Calls
• Deploy the Squid
• Conventions
• Type Bundles

Prerequisites

• node 16.x
• docker

Quickly running the sample

# 1. Install dependencies
npm ci

# 2. Compile typescript files
npm run build

# 3. Start target Postgres database
docker compose up -d

# 4. Apply database migrations from db/migrations
npx sqd db create
npx sqd db migrate

# 5. Now start the processor
node -r dotenv/config lib/processor.js

# 6. The above command will block the terminal
#    being busy with fetching the chain data, 
#    transforming and storing it in the target database.
#
#    To start the graphql server open the separate terminal
#    and run
npx squid-graphql-server

Setup for parachains

Subsquid provides Squid Archive data sources for most parachains. Use lookupArchive(<network name>) to lookup the archive endpoint by the network name, e.g.

processor.setDataSource({
  archive: lookupArchive("basilisk")[0].url,
  //...
});

To make sure you're indexing the right chain one can additionally filter by genesis hash:

processor.setDataSource({
  archive: lookupArchive("basilisk", undefined, "0xa85cfb9b9fd4d622a5b28289a02347af987d8f73fa3108450e2b4a11c1ce5755")[0].url,
  //...
});

If the chain is not yet supported, please fill the form to submit a request.

Setup for devnets and testnets

Non-production chains, e.g. Devnets and Testnets are not supported by lookupArchive and one has to provide a local Squid Archive as a data source.

Inspect archive/.env and provide the websocket endpoint for your node. If the network requires custom type bundles (for older versions of Substrate), mount them as volumes in archive/docker-compose.yml and uncomment the relevant sections in archive/.env.

Then run (in a separate terminal window)

docker compose -f archive/docker-compose.yml up

Inspect your archive at http://localhost:4010/console. Run the processor with

processor.setDataSource({
  archive: `http://localhost:4010/v1/graphql`,
  chain: // your network endpoint here
});

To drop the archive, run

docker compose -f archive/docker-compose.yml down -v

Dev flow

1. Define database schema

Start development by defining the schema of the target database via schema.graphql. Schema definition consists of regular graphql type declarations annotated with custom directives. Full description of schema.graphql dialect is available here.

2. Generate TypeORM classes

Mapping developers use TypeORM EntityManager to interact with target database during data processing. All necessary entity classes are generated by the squid framework from schema.graphql. This is done by running npx sqd codegen command.

3. Generate database migration

All database changes are applied through migration files located at db/migrations. sqd(1) tool provides several commands to drive the process. It is all TypeORM under the hood.

# Connect to database, analyze its state and generate migration to match the target schema.
# The target schema is derived from entity classes generated earlier.
npx sqd db create-migration

# Create template file for custom database changes
npx sqd db new-migration

# Apply database migrations from `db/migrations`
npx sqd db migrate

# Revert the last performed migration
npx sqd db revert

# DROP DATABASE
npx sqd db drop

# CREATE DATABASE
npx sqd db create            

4. Generate TypeScript definitions for substrate events and calls

This is an optional part, but it is very advisable.

Event, call and runtime storage data comes to mapping handlers as a raw untyped json. While it is possible to work with raw untyped json data, it's extemely error-prone and moreover the json structure may change over time due to runtime upgrades.

Squid framework provides tools for generation of type-safe, spec version aware wrappers around events, calls and runtime storage items. Typegen generates type-safe classes in types/events.ts, types/calls.ts and types/storage.ts respectively, with constructors taking XXXContext interfaces as the only argument. All historical runtime upgrades are accounted out of the box. A typical usage is as follows (see src/processor.ts):

function getTransferEvent(ctx: EventHandlerContext): TransferEvent {
  // instantiate the autogenerated type-safe class for Balances.Transfer event
  const event = new BalancesTransferEvent(ctx);
  // for each runtime version, reduce the data to the common interface
  if (event.isV1020) {
    const [from, to, amount] = event.asV1020;
    return { from, to, amount };
  } else if (event.isV1050) {
    const [from, to, amount] = event.asV1050;
    return { from, to, amount };
  } else {
    const { from, to, amount } = event.asV9130;
    return { from, to, amount };
  }
}

Generation of type-safe wrappers for events, calls and storage items is currently a two-step process.

First, you need to explore the chain to find blocks which introduce new spec version and fetch corresponding metadata.

npx squid-substrate-metadata-explorer \
  --chain wss://kusama-rpc.polkadot.io \
  --archive https://kusama.indexer.gc.subsquid.io/v4/graphql \
  --out kusamaVersions.json

In the above command --archive parameter is optional, but it speeds up the process significantly. From scratch exploration of kusama network without archive takes 20-30 minutes.

You can pass the result of previous exploration to --out parameter. In that case exploration will start from the last known block and thus will take much less time.

After chain exploration is complete you can use squid-substrate-typegen(1) to generate required wrappers.

npx squid-substrate-typegen typegen.json

Where typegen.json config file has the following structure:

{
  "outDir": "src/types",
  "chainVersions": "kusamaVersions.json", // the result of chain exploration
  "typesBundle": "kusama", // see types bundle section below
  "events": [ // list of events to generate
    "balances.Transfer"
  ],
  "calls": [ // list of calls to generate
    "timestamp.set"
  ],
  "storage": [
    "System.Account" // list of storage items. To generate wrappers for all storage items, set "storage": true
  ]
}

Deploy the Squid

Subsquid offers a free hosted service for deploying your Squid. First, build and run the docker image locally and fix any error or missing files in Dockerfile:

bash scripts/docker-run.sh # optionally specify DB port as an argument

After the local run, follow the instructions for obtaining a deployment key and submitting the Squid to Aquarium.

Project conventions

Squid tools assume a certain project layout.

• All compiled js files must reside in lib and all TypeScript sources in src. The layout of lib must reflect src.
• All TypeORM classes must be exported by src/model/index.ts (lib/model module).
• Database schema must be defined in schema.graphql.
• Database migrations must reside in db/migrations and must be plain js files.
• sqd(1) and squid-*(1) executables consult .env file for a number of environment variables.

Types bundle

Substrate chains which have blocks with metadata versions below 14 don't provide enough information to decode their data. For those chains external type definitions are required.

Type definitions (typesBundle) can be given to squid tools in two forms:

1. as a name of a known chain (currently only kusama)
2. as a json file of a structure described below.

{
  "types": {
    "AccountId": "[u8; 32]"
  },
  "typesAlias": {
    "assets": {
      "Balance": "u64"
    }
  },
  "versions": [
    {
      "minmax": [0, 1000], // block range with inclusive boundaries
      "types": {
        "AccountId": "[u8; 16]"
      },
      "typesAlias": {
        "assets": {
          "Balance": "u32"
        }
      }
    }
  ]
}

• .types - scale type definitions similar to polkadot.js types
• .typesAlias - similar to polkadot.js type aliases
• .versions - per-block range overrides/patches for above fields.

All fields in types bundle are optional and applied on top of a fixed set of well known frame types.

Differences from polkadot.js

Polkadot.js provides lots of specialized classes for various types of data. Even primitives like u32 are exposed through special classes. In contrast, squid framework works only with plain js primitives and objects. This allows to decrease coupling and also simply dictated by the fact, that there is not enough information in substrate metadata to distinguish between interesting cases.

Account addresses is one example where such difference shows up. From substrate metadata (and squid framework) point of view account address is simply a fixed length sequence of bytes. On other hand, polkadot.js creates special wrapper for account addresses which aware not only of address value, but also of its ss58 formatting rules. Mapping developers should handle such cases themselves.

Graphql server extensions

It is possible to extend squid-graphql-server(1) with custom type-graphql resolvers and to add request validation. More details will be added later.

Disclaimer

This is alpha-quality software. Expect some bugs and incompatible changes in coming weeks.