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Version: Firesquid

Create a Simple Squid


The goal of this tutorial is to guide you through creating and customizing a simple squid (API) using the Subsquid framework. The blockchain queried in this example will be the Crust storage network and our final objective will be to observe which files have been added and deleted from the network. Additionally, our squid will be able to tell us the groups joined and the storage orders placed by a given account.

We will start by forking the Subsquid squid template, then go on to run the project, define a schema, and generate TypeScript interfaces. From there, we will be able to interact directly with the Archive, and extract a types bundle from Crust's own library.

We expect that experienced software developers should be able to complete this tutorial in around 10-15 minutes. For reference, you can review the final result of this tutorial here.


The minimum requirements for this tutorial are as follows:

Fork the template

First things first! To fork the squid template and save it to your own GitHub account visit this repository and click the 'Fork' button:

How to fork a repository on GitHub

Next, clone the fork.

git clone<account>/squid-template.git

Don't forget to replace <account> in the repository with your own account information

Run the project

Now you can follow the quickstart guide to get the project up and running. In case you're in a hurry, here's a list of commands to run in quick succession:

npm ci
npm run build
make up
make migrate
make process
# open a separate terminal for this next command
make serve

These commands are intended for the first time you run the project. Please note that some of these commands, including make up and make migrate, could throw a warning or an error. This is because the container will already be running and migration will have been applied.

For the purposes of this tutorial, running the project is not strictly necessary. If you would like to skip ahead, we recommend at least running the Postgres container using the make up command.

Define the schema

In order to customize the project, we will need to make changes to the schema and define the Entities that we would like to track.

As stated above, we intend to track:

  • Files added and deleted from the chain;
  • Groups joined by a certain account;
  • Storage orders placed by a certain account.

To do this, we will make the following changes to schema.graphql:

type Account @entity {
id: ID! #Account address
workReports: [WorkReport] @derivedFrom(field: "account")
joinGroups: [JoinGroup] @derivedFrom(field: "member")
storageOrders: [StorageOrder] @derivedFrom (field: "account")

type WorkReport @entity {
id: ID! #event id
account: Account!
addedFiles: [[String]]
deletedFiles: [[String]]
extrinsicId: String
createdAt: DateTime!
blockHash: String!
blockNum: Int!

type JoinGroup @entity {
id: ID!
member: Account!
owner: String!
extrinsicId: String
createdAt: DateTime!
blockHash: String!
blockNum: Int!

type StorageOrder @entity {
id: ID!
account: Account!
fileCid: String!
extrinsicId: String
createdAt: DateTime!
blockHash: String!
blockNum: Int!

Notice that the Account entity is almost completely derived. It is there to tie the other three entities together.


Refer to this article if you are unsure which events and extrinsics to use for the handlers in your project.

To finalize this step, run the codegen tool:

make codegen

This will automatically generate TypeScript Entity classes for our schema. They can be found in the src/model/generated folder of the project.

Generate TypeScript interfaces

Refer here to learn how to generate TypeScript wrappers for Events and Extrinsics.

Chain exploration


In most cases, it is recommended to skip this section, which demonstrates how to manually carry out chain exploration. You may choose to scroll directly to the Typegen section below.

It is important is to pay attention to the chain, archive and out parameters for the purposes of this tutorial. In this Crust example, the following applies:

  • chain refers to the WebSocket address of the Crust blockchain.
  • archive refers to the Archive that is synchronized with the Crust blockchain.
  • out refers to the output file.

It is convention to include the name of the blockchain in the name of the output file. This is useful when multiple chains are handled in a single project or folder.

npx squid-substrate-metadata-explorer \
--chain wss:// \
--archive \
--out crustVersions.json

In this example, the output can be viewed in the crustVersions.json file. Although the metadata field is intelligible, it is worth noting that, at the time of this tutorial's creation, there exist 13 different versions. This means that the Runtime has changed 13 times.

It remains to be seen if this has had any impact on the definitions of the Events we are interested in.

Types bundle

The types of Crust's blockchain have not yet been integrated into Squid's library. For the new SquidDev, this offers a great opportunity to follow this mini-guide. In that tutorial, you will learn how to create extract the types bundle from Crust's own library and create an example project in Subsquid's required format.


Update: the "Crust" types bundle has now been added to Subsquid's list of built-ins. However, it may still be worthwhile to learn how to create create and utilize a types bundle JSON file when building with Subsquid.

Here is the end result. Copy it and paste it into a file named `crustTypesBundle.json`

Events wrappers generation

Good news! Subsquid's recent "FireSquid" release enables us to collapse metadata exploration and the above type-safe wrappers generation section into a single step. We can do this by specifying the URL of the relevant Archive in the specVersion field of the typegen.json config file.

By doing this, we no longer have to launch the metadata-explore command from the previous section. We will be able to generate type-safe interfaces with only one command, as explained below.

This is the best course of action, and the advised procedure going forward. This is because the newest version of Archives stores the chain's metadata information. The typegen command is able to leverage this stored metadata.

That being said, to adapt it to our purposes, we still need to make a few changes to the typegen.json configuration file. We do that by specifying the events that we are interested in.

Please note: Doing this requires knowledge of the blockchain itself and some research may be required. In the case of this example, the events are:

  • WorksReportSuccess from the swork pallet
  • JoinGroupSuccess from the same pallet
  • FileSuccess from the market pallet
"outDir": "src/types",
"specVersions": "",
"events": [
"calls": []

If you would like to perform the metadata exploration step manually and produce the resulting JSON file you can do so by following the instructions in the previous section. You can then make use of the generated file by changing the specVersions field in `typegen.json, launching the command in a console.

"specVersions": "crustVersions.json",

Doing this may be useful for manual inspection, debugging, or for simple consultation.

Finally, you may run the following command to generate type-safe TypeScript wrappers around the metadata

make typegen

The end result is in the src/types/events.ts file (we only defined Events in our typegen.json) and should look something like this:

Define and bind Event Handlers

After having obtained wrappers for Events and the metadata changes across different Runtime versions, it's finally time to define Handlers for these Events and attach them to our Processor. This is done in the src/processor.ts file of the project folder.

We will ultimately end up replacing the code in this file almost entirely, leaving only a few useful pieces. However, we are going to take a step-by-step approach, showing where essential changes have to be made. The final result will be visible at the end of this section.

First, in order to be able to use them in our code, we need to import the generated Entity model classes. Then, we will need the type definitions of Crust events, so that they can be used as wrappers.

Let's replace the previous models and the types imported at the top of our file with these two lines:

import  {Account, WorkReport, JoinGroup, StorageOrder} from './model/generated'
import { MarketFileSuccessEvent, SworkJoinGroupSuccessEvent, SworkWorksReportSuccessEvent } from './types/events'

Next, we need to customize the processor by setting the correct Archive as a Data Source and by specifying the Events we would like to index. This is done by applying the necessary changes to the first few lines of code after the imports.

Ultimately, it should look like this:

const processor = new SubstrateBatchProcessor()
archive: lookupArchive("crust", { release: "FireSquid" }),
.setBlockRange({ from: 583000 })
.addEvent("Market.FileSuccess", {
data: { event: { args: true , extrinsic: true, call: true} },
} as const)
.addEvent("Swork.JoinGroupSuccess", {
data: { event: { args: true , extrinsic: true, call: true} },
} as const)

Take note of the addEvent functions here. In the first two cases, we have added the extrinsic and call fields to the object. This signals to the processor that we are requesting this additional information. In the third function call, for the Swork.WorksReportSuccess event, we omitted the DataSelection object. This means we don't want to filter incoming information at all.

Since the added and deleted files are matrices, we are now, for our own convenience, going to need to declare a function. Simply add this code to the src/processor.ts file:

function stringifyArray(list: any[]): any[] {
let listStr: any[] = [];
for (let vec of list) {
for (let i = 0; i < vec.length; i++) {
vec[i] = String(vec[i]);
return listStr;

The declared Item and Ctx types are still useful, so we are going to keep them. Let's skip for now the call - we are going to come back to it in a second - and scroll down to the getTransfers function. In the template repository, this function loops through the items contained in the context, extracts the Event's data - which is stored in an Interface - and builds a list of these interfaces.

For this project, we need to do something similar, but not exactly the same: in order to process the three events we want to index, we need to extract Event data from the passed context, depending on the Event's name and store that information. But this time, we are saving the data directly to the database models, and we also need to handle the Account information separately, and we'll look at how it is dealt with in a moment.

We still need the AccountIds, though, so we are building some special interfaces to keep track of the rapport between an AccountId and the data related to it. Let's start with deleting the TransferEvent interface and defining this, instead:

type Tuple<T,K> = [T,K];
interface EventInfo {
joinGroups: Tuple<JoinGroup, string>[];
marketFiles: Tuple<StorageOrder, string>[];
workReports: Tuple<WorkReport, string>[];
accountIds: Set<string>;

Now, let's take the getTransfers function. Remove it and replace it with the below snippet. As described earlier, this will:

  • extract Event information in a different manner for each Event (using the to distinguish between them)
  • store Event information in a database Model and map it to the accountId
  • store the accountId in the set of IDs we are collecting
function getEvents(ctx: Ctx): EventInfo {
let events: EventInfo = {
joinGroups: [],
marketFiles: [],
workReports: [],
accountIds: new Set<string>(),
for (let block of ctx.blocks) {
for (let item of block.items) {
if ( === "Swork.JoinGroupSuccess") {
const e = new SworkJoinGroupSuccessEvent(ctx, item.event);
const memberId = ss58.codec("crust").encode(e.asV1[0]);
events.joinGroups.push([new JoinGroup({
owner: ss58.codec("crust").encode(e.asV1[1]),
blockHash: block.header.hash,
blockNum: block.header.height,
createdAt: new Date(block.header.timestamp),
extrinsicId: item.event.extrinsic?.id,
}), memberId]);

// add encountered account ID to the Set of unique accountIDs
if ( === "Market.FileSuccess") {
const e = new MarketFileSuccessEvent(ctx, item.event);
const accountId = ss58.codec("crust").encode(e.asV1[0]);
events.marketFiles.push([new StorageOrder({
fileCid: toHex(e.asV1[1]),
blockHash: block.header.hash,
blockNum: block.header.height,
createdAt: new Date(block.header.timestamp),
extrinsicId: item.event.extrinsic?.id,
}), accountId]);

// add encountered account ID to the Set of unique accountIDs
if ( === "Swork.WorksReportSuccess") {
const e = new SworkWorksReportSuccessEvent(ctx, item.event);
const accountId = ss58.codec("crust").encode(e.asV1[0]);

const addedExtr =;
const deletedExtr =;

const addedFiles = stringifyArray(addedExtr);
const deletedFiles = stringifyArray(deletedExtr);

if (addedFiles.length > 0 || deletedFiles.length > 0) {
events.workReports.push([new WorkReport({
addedFiles: addedFiles,
deletedFiles: deletedFiles,
blockHash: block.header.hash,
blockNum: block.header.height,
createdAt: new Date(block.header.timestamp),
extrinsicId: item.event.extrinsic?.id,
}), accountId]);

// add encountered account ID to the Set of unique accountIDs
return events;

Notice that we did not use a Map<string, > object. This is because there could be multiple entries for a single accountId. What we care about storing, in this case, is the relationship between the event data - stored in a model - and the accountId which is related to it. This way, when the Account model for a accountId is created, we can add that information to the Event model.

When all of this is done, we want to treat the set of accountIds, create a database Model for each of them, then go back and add the Account information in all the Event Models. For this we purpose we are going to re-use the existing getAccount function. Finally, save all the created and modified database models.

Take the code inside and change it so that it looks like this: TypeormDatabase(), async (ctx) => {
const events = getEvents(ctx);

let accounts = await
.findBy(Account, { id: In([]) })
.then((accounts) => {
return new Map( => [, a]));

for (const jg of events.joinGroups) {
const member = getAccount(accounts, jg[1]);
// necessary to add this field to the previously created model
// because now we have the Account created.
jg[0].member = member;

for (const mf of events.marketFiles) {
const account = getAccount(accounts, mf[1]);
// necessary to add this field to the previously created model
// because now we have the Account created.
mf[0].account = account;

for (const wr of events.workReports) {
const account = getAccount(accounts, wr[1]);
// necessary to add this field to the previously created model
// because now we have the Account created.
wr[0].account = account;

await => el[0]));
await => el[0]));
await => el[0]));

Here is the end result, in case you missed something

A repository with the entire project is also available on GitHub. If you like it, please leave a ⭐

Apply changes to the Database

Squid projects automatically manage the database connection and schema via an ORM abstraction. As such, we need to use the provided automated tools to manage the database schema and migrations.

Remove default migration

First, we need to get rid of the template's default migration:

rm -rf db/migrations/*.js

Then, in order to have a database to which we can connect, we must make sure that the Postgres docker container is running, then run the following commands:

npx squid-typeorm-migration generate
npx squid-typeorm-migration apply

These will:

  1. create the initial migration by looking up the schema we defined in the previous chapter;
  2. apply the migration.

Launch the project

It's finally time to run the project! First, let's build the code

npm run build

And then launch the processor (this will block the current terminal)

node -r dotenv/config lib/processor.js

Launch the GraphQL server (in a separate command line console window)

npx squid-graphql-server

Now you can see the resuls of our hard work by visiting the localhost:4350/graphql URL in a browser and accessing the GraphiQL console.

From this window, we can perform queries. This one displays which files have been added or deleted by an account:

query AccountFiles{
accountById(id: <accountID>) {
workReports {

It is advisable to search for an Account first and grab its ID.


This sample project is actually a real integration, developed by our very own Mikhail Shulgin. Credit for building it and helping with the guide goes to him.