Squid template project

A starter Squid project to demonstrate its structure and conventions. It accumulates kusama account transfers and serves them via GraphQL API.

Summary

• Quickstart
• Migrate to FireSquid
• Public archives for Parachains
• Self-hosted archive
• 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
• npm -- note that yarn package manager is not supported

Quickly running the sample

Example commands below use sqd. Please install it before proceeding.

# 1. Update Squid SDK and install dependencies
npm run update
npm ci

# 2. Compile typescript files
sqd build

# 3. Start target Postgres database and detach
sqd up

# 4. Start the processor
sqd process

# 5. The command above 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
sqd serve

Public archives for Parachains

Subsquid provides archive data sources for most parachains, with API playgrounds available at https://graphql-console.subsquid.io/?graphql_api=<archive_endpoint_url>.

The list of public archive data source endpoints is also maintained in the @subsquid/archive-registry npm package for programmatic access. Use lookupArchive(<network name>, <lookup filters>) to look up the archive endpoint by the network name, e.g.

processor.setDataSource({
  archive: lookupArchive("kusama", { release: "FireSquid" })
  //...
});

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

processor.setDataSource({
  archive: lookupArchive("kusama", { 
    release: "FireSquid", 
    genesis: "0xb0a8d493285c2df73290dfb7e61f870f17b41801197a149ca93654499ea3dafe" 
  }),
  //...
});

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

Self-hosted archive

To run an archive locally, inspect archive/docker-compose.yml and provide the WebSocket endpoint for your node, then start it with

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

To drop the archive, run

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

The archive gateway will be started at port 8888 and it can immediately be used with the processor (even if it's not in sync):

processor.setDataSource({
  archive: `http://localhost:8888/graphql`,
});

Additionally, an explorer GraphQL API and a playground will be started at http://localhost:4350/graphql. While optional, it's a useful tool for debugging and on-chain data exploration.

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 entities to interact with the target database during data processing. All necessary entity classes are generated by the squid framework from schema.graphql. This is done by running npx squid-typeorm-codegen command.

3. Generate database migration

All database changes are applied through migration files located at db/migrations. squid-typeorm-migration(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.
# Don't forget to compile your entity classes beforehand!
npx squid-typeorm-migration generate

# Create template file for custom database changes
npx squid-typeorm-migration create

# Apply database migrations from `db/migrations`
npx squid-typeorm-migration apply

# Revert the last performed migration
npx squid-typeorm-migration revert         

4. Generate TypeScript definitions for substrate events, calls and storage

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

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

Squid framework provides tools for generating type-safe wrappers around events, calls and runtime storage items for each historical change in the spec version.

Typical usage looks as follows:

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

To generate type-safe wrappers for events, calls and storage items, use squid-substrate-typegen(1). It expects a config file of the following structure:

{
  "outDir": "src/types",
  // List of chain spec versions.
  // Can be given as:
  //    1. Squid archive URL
  //    2. JSON lines file created by `squid-substrate-metadata-explorer(1)`
  "specVersions": "https://kusama.archive.subsquid.io/graphql",
  "events": [ // list of events to generate. To generate all events, set "events": true.
    "Balances.Transfer"
  ],
  "calls": [ // list of calls to generate. To generate all calls, set "calls": true.   
    "Timestamp.set"
  ],
  "storage": [
    "System.Account" // list of storage items. To all storage items, set "storage": true
  ]
}

In the current template, the list of spec versions is specified as an archive URL. However, one can do without archive or simply pre-download spec versions via squid-substrate-metadata-explorer(1) tool.

# Explore the chain (may take some time)
npx squid-substrate-metadata-explorer \
  --chain wss://kusama-rpc.polkadot.io \
  --out kusamaVersions.jsonl
  
# Download spec versions from archive
npx squid-substrate-metadata-explorer \
  --archive https://kusama.archive.subsquid.io/graphql \
  --out kusamaVersions.jsonl

Deploy the Squid

After a local run, obtain a deployment key by signing into Aquarium and run

npx sqd auth -k YOUR_DEPLOYMENT_KEY

Next, inspect the Squid CLI help to deploy and manage your squid:

npx sqd squid --help

For more information, consult the Deployment Guide.

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.
• squid-*(1) executables consult .env file for a number of environment variables.

Types bundle

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

Subsquid tools include definitions for many chains, however sometimes external definitions are still required.

You can pass them as a special json file (types bundle) of the following structure:

{
  "types": {
    "AccountId": "[u8; 32]"
  },
  "typesAlias": {
    "assets": {
      "Balance": "u64"
    }
  },
  "versions": [
    {
      "minmax": [0, 1000], // spec version 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 the type bundle are optional and applied on top of a fixed set of well-known frame types.

Note, that although the structure of subsquid types bundle is very similar to the one from polkadot.js, those two are not fully compatible.

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, the squid framework works only with plain js primitives and objects. For instance, account data is passed to the handler context as a plain byte array. To convert it into a standard human-readable format one should explicitly use a utility lib @subsquid/ss58:

    // ...
    from: ss58.codec('kusama').encode(rec.from),
    to: ss58.codec('kusama').encode(rec.to),

Graphql server extensions

It is possible to extend squid-graphql-server(1) with custom type-graphql resolvers and to add request validation. For more details, consult docs