Lesson 3: How to Index a Substrate Event
Lesson 3: How to Index a Substrate Event
This lesson explains how to index Substrate native events alongside Moonbeam data. We will alter the code by adding a collatorJoined event and updating schema.graphql, project.yaml and mappingHandlers.ts accordingly.
Changing the Project
Note
In this lesson we will alter the code.
Manifest
Let's start with adding new data source on the bottom of project.yaml file. This will allow a new handler collatorJoined to be used to extract data from the chain. The handler name has to match the name of corresponding function in mappinghandlers.ts file. Pay attention to different content of kind, module and method specification.
- kind: substrate/Runtime
startBlock: 69218
mapping:
file: "./dist/index.js"
handlers:
- handler: collatorJoined
kind: substrate/EventHandler
filter:
module: parachainStaking
method: JoinedCollatorCandidates
Your entire Manifest file should look like this:
specVersion: 1.0.0
name: moonbeam-evm-starter
version: 0.0.1
runner:
node:
name: "@subql/node"
version: ">=0.35.0"
query:
name: "@subql/query"
version: ">=0.16.0"
description: Moonbeam / SubQuery Course — Building dApps with the help of SubQuery
repository: "https://github.com/subquery/tutorials-frontier-evm-starter"
schema:
file: ./schema.graphql
network:
chainId: "0x401a1f9dca3da46f5c4091016c8a2f26dcea05865116b286f60f668207d1474b"
endpoint: "wss://moonriver.api.onfinality.io/public-ws"
dictionary: "https://api.subquery.network/sq/subquery/moonriver-dictionary"
chaintypes:
file: ./dist/chaintypes.js
dataSources:
- kind: substrate/FrontierEvm
startBlock: 424026
processor:
file: ./node_modules/@subql/frontier-evm-processor/dist/bundle.js
options:
abi: erc20
address: "0x6bd193ee6d2104f14f94e2ca6efefae561a4334b"
assets:
erc20:
file: ./erc20.abi.json
mapping:
file: ./dist/index.js
handlers:
- handler: handleFrontierEvmEvent
kind: substrate/FrontierEvmEvent
filter:
topics:
- "Transfer(address indexed from,address indexed to,uint256 value)"
- null
- null
- null
- handler: handleFrontierEvmCall
kind: substrate/FrontierEvmCall
filter:
function: "approve(address to,uint256 value)"
- kind: substrate/Runtime
startBlock: 69218
mapping:
file: "./dist/index.js"
handlers:
- handler: collatorJoined
kind: substrate/EventHandler
filter:
module: parachainStaking
method: JoinedCollatorCandidates
Note
Find more information about Polkadot specific methods in Polkadot Explorer.
Schema GraphQl
Next steps would be to add a new entity — Collator - to schema.graphql file. Apart from the required id it should also include another required property - joinedDate of data type Date.
type Collator @entity {
id: ID! # Collator address
joinedDate: Date!
}
The entire file should look like this:
type Transaction @entity {
id: ID! # Transaction hash
value: BigInt!
to: String!
from: String!
contractAddress: String!
}
type Approval @entity {
id: ID! # Transaction hash
value: BigInt!
owner: String!
spender: String!
contractAddress: String!
}
type Collator @entity {
id: ID! # Collator address
joinedDate: Date!
}
Important
Remember to regerate associated typescript after any change in the schema.grapql.
yarn codegen
npm run-script codegen
Next step would be to create a proper function that allow creating collators and saving all the needed data in our database.
Mapping functions
The final step would be to add collatorJoined() function to mappingsHanderls.ts file. This function is responsible for getting the data from the chain, creating an entity and saving it in the database with all the information we need.
// Create Collator
export async function collatorJoined(event: SubstrateEvent): Promise<void> {
const address = event.extrinsic.extrinsic.signer.toString();
const collator = Collator.create({
id: address,
joinedDate: event.block.timestamp,
});
await collator.save();
}
Your file should look like this:
import { Approval, Collator, Transaction } from "../types";
import {
FrontierEvmEvent,
FrontierEvmCall,
} from "@subql/frontier-evm-processor";
import { BigNumber } from "ethers";
import { SubstrateEvent } from "@subql/types";
// Setup types from ABI
type TransferEventArgs = [string, string, BigNumber] & {
from: string;
to: string;
value: BigNumber;
};
type ApproveCallArgs = [string, BigNumber] & {
_spender: string;
_value: BigNumber;
};
// Create Transaction
export async function handleFrontierEvmEvent(
event: FrontierEvmEvent<TransferEventArgs>,
): Promise<void> {
const transaction = new Transaction(event.transactionHash);
transaction.value = event.args.value.toBigInt();
transaction.from = event.args.from;
transaction.to = event.args.to;
transaction.contractAddress = event.address;
await transaction.save();
}
// Create Approval
export async function handleFrontierEvmCall(
event: FrontierEvmCall<ApproveCallArgs>,
): Promise<void> {
const approval = new Approval(event.hash);
approval.owner = event.from;
approval.value = event.args._value.toBigInt();
approval.spender = event.args._spender;
approval.contractAddress = event.to;
await approval.save();
}
// Create Collator
export async function collatorJoined(event: SubstrateEvent): Promise<void> {
const address = event.extrinsic.extrinsic.signer.toString();
const collator = Collator.create({
id: address,
joinedDate: event.block.timestamp,
});
await collator.save();
}
Query
Open your browser and head to http://localhost:3000. Use GraphQL playground to query your data. Expand previous query by adding collators on the bottom:
query {
approvals(first: 5) {
nodes {
id
value
owner
spender
}
}
transactions(first: 5) {
nodes {
id
value
to: id
from: id
}
}
collators(last: 5) {
nodes {
id
joinedDate
leaveDate
}
}
}