mapping.ts

import {
  AddSubmission,
  VouchAdded,
  VouchRemoved
} from "../generated/ProofOfHumanity/ProofOfHumanity";

import { User } from "../generated/schema";

export function handleVouchAdded(event: VouchAdded): void {
  let user = User.load(event.transaction.from.toHex());

  if (user == null) return;

  let vouches = user.vouches;
  vouches.push(event.params._submissionID.toHex());
  user.vouches = vouches;
  user.save();
}

export function handleAddSubmission(event: AddSubmission): void {
  let user = new User(event.params._submissionID.toHex());
  user.vouches = new Array<string>();
  user.registerDate = event.block.timestamp;
  user.save();
}

schema.graphql

type User @entity {
  id: ID!
  vouches: [User!]!
  registerDate: BigInt!
}