How to Filter Multiple Events with Connex

Connex is a powerful tool for developers to interact with the VeChainThor blockchain. When filtering events from a single contract, the Account Visitor can be used. However, in some cases, multiple events or sources need to be filtered. In this blog post, we'll explore how to use connex.thor.filter to execute multiple filters in a single call.

Preparation

Before we dive into the code, let's set up the necessary imports and example ABI:

import Connex from "@vechain/connex";
import { abi } from "thor-devkit";
 
const connex = new Connex({
  node: "https://mainnet.veblocks.net",
  network: "main"
});
 
const ABI = {
    "anonymous": false,
    "inputs": [
        {
            "indexed": true,
            "name": "_from",
            "type": "address"
        },
        {
            "indexed": true,
            "name": "_to",
            "type": "address"
        },
        {
            "indexed": false,
            "name": "_value",
            "type": "uint256"
        }
    ],
    "name": "Transfer",
    "type": "event"
}

Encoding the Request

To create an event instance, we'll use the abi package:

const transferEvent = new abi.Event(ABI)

The most important methods are encode() and decode(), as well the signature attribute.

encode() Parameters

The encode() method maps the object to the ABI input arguments, returning a list of topics that can be used for filtering.

Note: Only indexed arguments can be filtered.

const topics = transferEvent.encode({ _to: "0x04Ad3f13050cc766169433062BcDbB367B616986" })

filter()

The returned topics can be used to define the filter:

const events = await connex.thor
	.filter("event", [
	  {
	    address: "0x0000000000000000000000000000456E65726779",
	    topic0: topics[0] || undefined,
	    topic1: topics[1] || undefined,
	    topic2: topics[2] || undefined,
	    topic3: topics[3] || undefined,
	    topic4: topics[4] || undefined
	  }
	])
	.apply(0, 20);

Notably, we can exclude the address parameter to apply the search on all contracts.

Decoding the Request

The decoding process needs to be manually handled for every event returned. decode() expects the event data and the topics as parameters because the topics contain the indexed values, while data contains the rest. Both need to be decoded separately and then combined to provide the full decoded information:

const logs = events.map(event => {
  return {
    ...event,
    decoded: transferEvent.decode(event.data, event.topics)
  };
})

Conclusion

Using connex.thor.filter, we can filter events from multiple sources or multiple events in a single call. By manually handling the encoding and decoding process with the help of thor-devkit, we can retrieve the necessary information from the blockchain. Connex provides a powerful toolset for to interact with the vechain, and mastering it can greatly enhance your dApp development experience.