gatsby-node.ts

import type { GatsbyNode } from 'gatsby'
import { DataJson } from './graphql-types'
import { createRemoteFileNode } from 'gatsby-source-filesystem'

export const createSchemaCustomization: GatsbyNode['createSchemaCustomization'] = ({ actions }) => {
  const { createTypes } = actions

  createTypes(`
    type DataJson implements Node {
      data: DataJson
      featuredImg: File @link(from: "fields.localFile")
    }
  `)
}

export const onCreateNode: GatsbyNode<DataJson>['onCreateNode'] = async ({
  node,
  actions: { createNode, createNodeField },
  createNodeId,
  getCache,
}) => {
  if (node.internal.type === 'DataJson' && node?.full_picture != null) {
    try {
      const fileNode = await createRemoteFileNode({
        url: node?.full_picture, // string that points to the URL of the image
        parentNodeId: node.id, // id of the parent node of the fileNode you are going to create
        createNode, // helper function in gatsby-node to generate the node
        createNodeId, // helper function in gatsby-node to generate the node id
        getCache,
      })

      if (fileNode) {
        createNodeField({ node, name: 'localFile', value: fileNode.id })
        console.log('File created for featuredImg. ')
      }
    } catch (error) {
      console.log("Couldn't create featuredImg. ")
    }
  }
}