TypeORM Upsert

Say you have a TypeORM entity Post and you want to atomically upsert:

import { Upsert } from 'typeorm-upsert'
import { SnakeCase } from 'snake-case'

const post: Post = { ... }

(async () => {
    const upserted_post = await Upsert(
        Post, 
        post,
        "id",   // primary-key to upsert on

        // optional params
        {
            key_naming_transform: SnakeCase, // arbitrarily transform keys before UPSERT
            do_not_upsert: ['created_at']    // exclude non-nullable keys from UPDATE that are required in the event of an INSERT operation
        }
    )

    console.log(upserted_post) // prints the finished version of `Post`
})

Tested with PostgreSQL 9.5+. Contributors welcome.