Collect a Post

In this section you'll learn how to implement the Collect Essence feature. Previously you've learned that creating a post means registering an essence, but the process of minting and transferring the NFT is actually executed when a user collects the post.

GraphQL mutations

To collect an essence, meaning to collect a post, is a two step process and requires two GraphQL mutations: CreateCollectEssenceTypedData and Relay.

1. CreateCollectEssenceTypedData is used to present data to the user in a readable format:

graphql/CreateCollectEssenceTypedData.ts

import { gql } from "@apollo/client";

export const CREATE_COLLECT_ESSENCE_TYPED_DATA = gql`
    mutation CreateCollectEssenceTypedData(
        $input: CreateCollectEssenceTypedDataInput!
    ) {
        createCollectEssenceTypedData(input: $input) {
            typedData {
                id
                chainID
                sender
                data
                nonce
            }
        }
    }
`;

2. Relay is responsible for broadcasting the transaction, minting and transferring the NFT:

graphql/Relay.ts

import { gql } from "@apollo/client";

export const RELAY = gql`
    mutation Relay($input: RelayInput!) {
        relay(input: $input) {
            relayTransaction {
                id
                txHash
                typedData {
                    id
                    chainID
                    sender
                    data
                    nonce
                }
            }
        }
    }
`;

Collect a Post

Now that you set up the APIs required, you can implement the Collect feature. The approach is almost exactly the same as it was for Subscribe to Profile:

1. Get data in a readable format and the typedDataID for it;
2. Get the user to sign the message data and get its signature;
3. Call the relay and pass it the typedDataID and signature;

components/CollectBtn.tsx

/* Create typed data in a readable format */
const typedDataResult = await createCollectEssenceTypedData({
    variables: {
        input: {
            options: {
                chainID: chainID,
            },
            collector: account,
            profileID: profileID,
            essenceID: essenceID,
        },
    },
});

const typedData =
    typedDataResult.data?.createCollectEssenceTypedData?.typedData;
const message = typedData.data;
const typedDataID = typedData.id;

/* Get the signature for the message signed with the wallet */
const params = [account, message];
const method = "eth_signTypedData_v4";
const signature = await signer.provider.send(method, params);

/* Call the relay to broadcast the transaction */
const relayResult = await relay({
    variables: {
        input: {
            typedDataID: typedDataID,
            signature: signature,
        },
    },
});
const txHash = relayResult.data?.relay?.relayTransaction?.txHash;

If the collect process was successful, you can verify the transaction hash on goerli.etherscan.io.

You can also view the NFT when a user collects a post on testnets.opensea.io. You'll notice that the image for the NFT and all other details about it correspond to the details passed to the Metadata Schema fields (e.g. image_data, name, description, etc).

Next up you will dive deep into middlewares and learn how to set them. Let's start with Middleware for Subscribe.