save to file from database, node.js, knex.js, fastify

writeableStream

import { boomify } from '@hapi/boom';
import { Parser } from '@json2csv/plainjs';
import { Json2CSVBaseOptions } from '@json2csv/plainjs/dist/mjs/BaseParser';
import { FastifyReply } from 'fastify/types/reply';
import { Knex } from 'knex';
import { Transform } from 'stream';

export const writableStream = async (
    opts: Omit<Json2CSVBaseOptions<object, object>, 'ndjson'> | undefined,
    data: Knex.QueryBuilder<
        {},
        {
            _base: {};
            _hasSelection: false;
            _keys: string;
            _aliases: {};
            _single: false;
            _intersectProps: {};
            _unionProps: never;
        }[]
    >,
    reply: FastifyReply,
) => {
    let isCSVHeaderSent = false;
    const transform = new Transform({
        writableObjectMode: true,
        transform(chunk, encoding, callback) {
            if (isCSVHeaderSent && opts) {
                opts.header = false;
            }
            const parser = new Parser(opts);
            isCSVHeaderSent = true;
            this.push(parser.parse([chunk]) + '\n');
            callback();
        },
    });

    await data
        .stream(function (stream) {
            stream.pipe(transform);
        })
        .then(function () {
            reply.header('Content-Type', 'text/csv');
            return reply.send(transform);
        })
        .catch(function (e: any) {
            throw boomify(e as Error);
        });
};