Gabriela Ferrara gabidavila

Using Active Record migrations beyond SQLite

SQLite is really a good tool to set up quick proof of concepts and small applications, however it's not the most robust solution on the market to work with relational databases. In the open source community two databases take the top of the list: PostgreSQL and MySQL.

I did a small project for my studies, and I was using SQLite as I didn't need much out of it. Curious, I decided to see how the application would behave on the other databases and decided to try PostgreSQL and MySQL. I had two problems to solve, and this post is about the first one: how to deal with the migrations. They were as follows:

class CreateArtists < ActiveRecord::Migration[5.1]
  def change

	//receives an array, and the callback perform an operation
	//
	function reduce(array, callback, initialValue) {
	let acumulator = initialValue ? initialValue : array[0];
	let i = initialValue ? 0 : 1;

	for (; i < array.length; i++) {
	acumulator = callback(acumulator, array[i])
	}
	return acumulator

	class CreateSongs < ActiveRecord::Migration
	def change
	create_table :songs do \|t\|
	t.string :title
	t.integer :artist_id, limit: 8

	t.timestamps
	end

	add_index :songs, :title

	class CreateArtists < ActiveRecord::Migration
	def change
	create_table :artists do \|t\|
	t.string :name

	t.timestamps
	end

	add_index :artists, :name
	end

	SELECT
	`captains`.*
	FROM
	`captains`
	WHERE
	`captains`.`id` IN (SELECT
	`boats`.`captain_id`
	FROM
	`boats`
	WHERE

	SELECT
	`captains`.*
	FROM
	`captains`
	INNER JOIN
	`boats` ON `boats`.`captain_id` = `captains`.`id`
	INNER JOIN
	`boat_classifications` ON `boat_classifications`.`boat_id` = `boats`.`id`
	INNER JOIN
	`classifications` ON `classifications`.`id` = `boat_classifications`.`classification_id`

	INSERT INTO songs (title, artist_id, created_at, updated_at)
	VALUES ('We will Rock you', 21474836481, now(), now());