Eldora  Bradtke

Eldora Bradtke

1595504760

An Approach to JavaScript Object Schema Migration

Introduction

Recently, I found myself in a position where an application was heavily reliant on a state object. This is fairly typical for single page applications (SPAs) and can pose a challenge when your state object’s schema changes significantly and you have users that have data saved under an old schema.

In this post, I’ll explore a proof-of-concept solution I put together to explore the topic. While I’m sure there are schema migration tools in existence already, I figured this would be an interesting and educational exploration of the topic!

An Example Problem

Let’s say I’ve created an app in which there’s a user and that user can enter their pet type and breed. Upon launching the MVP, my state object looks something like this:

const state = {
  person: {
    name: 'Edgar',
    pets: {
      type: 'dog',
      name: 'Daffodil',
    },
  },
};

This works great for the MVP, but soon I realize I don’t want the pets property to live under the person property, but rather I want it to be it’s own propert under state. In other words, my ideal state might look like this:

const state = {
  person: {
    name: 'Edgar',
  },
  pets: {
    type: 'dog',
    name: 'Daffodil',
  },
};

While I’d like to simply be able to make this change in my SPA, I’m concerned that existing app users have my original schema saved somewhere (e.g., local storage, nosql, a JSON string, etc.). If I load that old data but my app expects the new schema, I may try to access properties in the wrong place (e.g., state.pets.type versus state.person.pets.type), causing issues.

Schema Migration to the Rescue!

Schema migration isn’t a new concept; it’s been used for quite some time to migrate database tables between different versions of applications. In this post, I’m going to use the same basic concepts behind schema migrations to migrate JavaScript objects.

Defining our Migration Array

Let’s define an array of migrations to run. Each migration will have a fromtoup, and down property. The from and to props will represent the lower and higher version respectively, and the up and down props will be functions that move a schema from the from version to the to version and vice-versa. That may sound a bit confusing, but I think it’ll make a bit more sense in the context of our person/pets example.

Let’s write the first migration.

const migrations = [
  {
    from: '1.0',
    to: '1.1',
    up: schema => {
      const newSchema = {
        version: '1.1',
        person: {
          name: schema.person.name,
        },
        pets: {
          ...schema.person.pets,
        },
      };
      return newSchema;
    },
    down: schema => {
      const newSchema = {
        version: '1.0',
        person: {
          ...schema.person,
          pets: { ...schema.pets },
        },
      };
      return newSchema;
    },
  },
];

If we have a version “1.0” schema, the up method of this object will convert that schema to “1.1”. Conversely, if we have a version “1.1” schema, the down method will convert that schema to “1.0”.

#javascript #programming

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An Approach to JavaScript Object Schema Migration
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MEAN Stack Tutorial MongoDB ExpressJS AngularJS NodeJS

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FreeBSD s3cmd failed [SSL CERTIFICATE_VERIFY_FAILED]

When I install s3cmd package on my FreeBSD system and try to use the s3cmd command I get the following error:

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How to install s3cmd on FreeBSD

Search for s3cmd package:

$ pkg search s3cmd

Execute the following command and make sure you install Python 3.x package as Python 2 will be removed after 2020:

$ sudo pkg install py37-s3cmd-2.1.0

Updating FreeBSD repository catalogue...
FreeBSD repository is up to date.
All repositories are up to date.
Checking integrity... done (0 conflicting)
The following 8 package(s) will be affected (of 0 checked):

New packages to be INSTALLED:
	libffi: 3.2.1_3
	py37-dateutil: 2.8.1
	py37-magic: 5.38
	py37-s3cmd: 2.1.0
	py37-setuptools: 44.0.0
	py37-six: 1.14.0
	python37: 3.7.8
	readline: 8.0.4

Number of packages to be installed: 8

The process will require 118 MiB more space.

Proceed with this action? [y/N]: y
[rsnapshot] [1/8] Installing readline-8.0.4...
[rsnapshot] [1/8] Extracting readline-8.0.4: 100%
[rsnapshot] [2/8] Installing libffi-3.2.1_3...
....
..
[rsnapshot] [8/8] Extracting py37-s3cmd-2.1.0: 100%
=====
Message from python37-3.7.8:

--
Note that some standard Python modules are provided as separate ports
as they require additional dependencies. They are available as:

py37-gdbm       databases/py-gdbm@py37
py37-sqlite3    databases/py-sqlite3@py37
py37-tkinter    x11-toolkits/py-tkinter@py37

#[object object] #[object object] #[object object] #[object object] #[object object] #[object object] #[object object]

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  • » Remove sendmail
  • » Install postfix
  • » Configuring postfix for SES
  • » Test postfix

Procedure to configure AWS SES with Postfix

Before getting started with Amazon SES and Postfix, you need to sign up for AWS, including SES. You need to verify your email address and other settings. Make sure you create a user for SES access and download credentials too.

Step 1 – Uninstall Sendmail if installed

If sendmail installed remove it. Debian/Ubuntu Linux user type the following apt command/apt-get command:

$`` sudo apt --purge remove sendmail

CentOS/RHEL user type the following yum command or dnf command on Fedora/CentOS/RHEL 8.x:

$`` sudo yum remove sendmail

$`` sudo dnf remove sendmail

Sample outputs from CentOS 8 server:

Dependencies resolved.
===============================================================================
 Package           Architecture  Version               Repository         Size
===============================================================================
Removing:
 sendmail          x86_64        8.15.2-32.el8         @AppStream        2.4 M
Removing unused dependencies:
 cyrus-sasl        x86_64        2.1.27-1.el8          @BaseOS           160 k
 procmail          x86_64        3.22-47.el8           @AppStream        369 k

Transaction Summary
===============================================================================
Remove  3 Packages

Freed space: 2.9 M
Is this ok [y/N]: y

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