addEntity to knex query with simplicity and clean code

index.js

var R = require('ramda');
var knex = require('knex')({
    client: 'pg',
    connection: {
        host: 'localhost',
        port: '35432',
        database: 'vamos',
        password: 'vamos',
        user: 'vamos',
    }
});


const withEntity = (qb, table, fk, alias = table) => qb.leftJoin(table, fk, `${table}.id`).select(knex.raw(`to_json(${table}) ${alias}`))

const queryWrapper = (query, resolver) => {

    let mappings = {};
    
    return {
        query,
        addContact(...path) {
            if (mappings.contact) throw new Error('addContact called twice');
            mappings.contact = path.length > 0 ? R.flatten(path) : ['contact'];

            query.modify(withEntity, 'contact', 'beuz.contact_id')
            return this;
        },
        addCompany(...path) {
            if (mappings.company) throw new Error('addCompany called twice');
            mappings.company = path.length > 0 ? R.flatten(path) : ['company'];

            query.modify(withEntity, 'company', 'contact.company_id')
            return this;
        },
        then(...args) {
            return query
                .map(row => {
                    const keys = Object.keys(mappings);                   
                    return keys.reduce((acc, key) => R.assocPath(mappings[key], row[key], acc), R.omit(keys, row));
                })
                .map(resolver)
                .then(...args);
        }
    }
}


const contactR = contact => ({
    id: contact.id,
    firstname: contact.firstname,
    lastname: contact.lastname,
    company: contact.company
});

const resolver = beuz => ({
    id: beuz.id,
    contact: contactR(beuz.contact),
})

const db = {
    getBeuz(filters, sqlParams) {
        return queryWrapper(knex('beuz').select('beuz.id').where('beuz.id', 1), resolver);
    },
}

const a = db.getBeuz({}, {})
  .addContact()
  .addCompany(['contact', 'company'])
  .then(res => {
      console.log(res);
  });