schema.js

import { makeExecutableSchema } from 'graphql-tools'
import { HubABI, AuctionABI, web3 } from '../contracts'

const schema = ...

const resolvers = {
    Auction: {
        // auction is an instance of the Auction contract wrapper
        itemName: auction => auction.methods.itemName().call(),
    },
    Query: {
        allAuctions: async () => {
            // create a reference to the hub contract we created earlier
            const hub = new web3.eth.Contract(HubABI, 'hub address from before')

            // build the list of auctions
            const auctions = []
            for (let i = 0; i < await hub.methods.auctionCount().call(); i++) {
                auctions.push(
                    new web3.eth.Contract(
                        AuctionABI,
                        await hub.methods.auctions(i).call()
                    )
                )
            }

            return auctions
        }
    },
}

export default makeExecutableSchema({
    typeDefs: schema,
    resolvers,
})