movingco/migrations/01_insert_example.js

const seedDb = require('../index')
const h = require('../helpers')

/**
 * What TYPE are you migrating?
 */ 
const mainType = h.types.post

module.exports = {
    up: async query => {
        const fromSeedDB = h.db(seedDb)
        const toCleanDB = h.db(query.sequelize)

        /**
         * Our base list of posts matching mainType to migrate
         */
        const matchingPosts = await fromSeedDB.wp_posts.findAll({
            where: {
                post_type: mainType,
                post_status: h.types.status
            }
        })
        const postsToWrite = h.getPostData(matchingPosts, mainType)

        /**
         * Attachments matching ID's in postsToWrite
         */
        const matchingAttachments = await h.findDescendants(
            postsToWrite,
            fromSeedDB.wp_posts,
            post => ({
                post_type: h.types.attachment,
                post_parent: post.ID
            })
        )
        const attachmentsToWrite = h.getPostData(matchingAttachments, h.types.attachment)

        /**
         * Attachments are POSTS too, so we combine the two lists
         * before we can find postmeta keys we care about
         *
         * 1. Meta keys are match anything in our h.metakeys list
         *    using opt.in to evaluate h.metakeys.indexOf(post)
         */
        const postmeta = await h.findDescendants(
            [...matchingPosts, ...matchingAttachments],
            fromSeedDB.wp_postmeta,
            post => ({
                post_id: post.ID,
                /* 1 */
                meta_key: h.metakeys
            })
        )
        const postmetaToWrite = h.getPostData(postmeta, false)
        
        /**
         * INSERT in our new db with some options
         * 1. First we insert our episode POST and attachments
         *    to the posts table
         * 2. Then we add our matching POSTMETA entries to
         *    the postmeta table
         */
        const createOptions = { validate: true }
        /* 1 */
        await toCleanDB.wp_posts.bulkCreate([
            ...postsToWrite,
            ...attachmentsToWrite
        ], createOptions)
        /* 2 */
        await toCleanDB.wp_postmeta.bulkCreate([
            ...postmetaToWrite
        ], createOptions)
    },

    down: async query => {
        // Do nothing...
    },
}