gatsby-node.js

const write = require("write");
const path = require("path");
const { printSchema } = require("gatsby/graphql");

exports.onPostBootstrap = async ({ store }, options) => {
  try {
    const defaultLocation = path.resolve(process.cwd(), "schema.graphql");
    const defaultGetSchema = async (obj) =>
      printSchema(obj, { commentDescriptions: true });
    const defaultWriteSchema = async (location, schema) =>
      write(location, schema);

    const location = options.dest || defaultLocation;
    const { schema: internalSchemaObj } = store.getState();
    const getSchema = options.getSchema || defaultGetSchema
    let schema = (await getSchema(internalSchemaObj));
    schema = options.adjustSchema ? await options.adjustSchema(schema) : schema;

    const writeSchema = options && options.writeSchema || defaultWriteSchema;
    await writeSchema(location, schema);

    console.log("[gatsby-plugin-extract-schema] Wrote schema");
  } catch (error) {
    console.error(
      "[gatsby-plugin-extract-schema] Failed to write schema: ",
      error
    );
  }
};