apollo-link-ethereum-example's Introduction

Apollo Link Ethereum Example App

This app demonstrates the use of apollo-link-ethereum

Live here (not much to see though ;)

Setup

$ yarn

Usage

Start the Create React App dev server:

$ yarn start

Now navigate to http://localhost:3000 in your browser. The app is hard-coded to mainnet, so MetaMask will not affect the output.

Highlights

First you should take note of apolloClient.js. This is where the EthereumLink is setup:

// apolloClient.js

export const abiMapping = new AbiMapping()
abiMapping.addAbi('MKR', mkrAbi)
abiMapping.addAddress('MKR', 1, '0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2')

const provider = new ethers.getDefaultProvider('homestead')

const ethersResolver = new EthersResolver({
  abiMapping,
  provider
})

const ethereumLink = new EthereumLink(ethersResolver)

// ...

export const apolloClient = new ApolloClient({
  cache,
  link: ApolloLink.from([stateLink, ethereumLink])
})

Next is to look at how we query Ethereum in App.js:

// src/App.js

const MKR_QUERY = gql`
  query MkrQuery {
    MKR @contract {
      totalSupply
      someonesBalance: balanceOf(address: "0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2")
      allEvents @pastEvents(fromBlock: "4620855", toBlock: 4621855)
    }
  }
`

class App extends Component {
  render() {
    return (
      <Query query={MKR_QUERY}>
        {/* ... */}
      </Query>
    )
  }
}

You'll notice the custom directives @contract and @pastEvents. These are defined by apollo-link-ethereum and will send the requests to the Ethereum blockchain.

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