billhimmelsbach/migration_hell

Migration Hell Drills

In this drill, we're going to explore migration hell. Please come along.

The #1 rule of migration hell is this:

DON'T MODIFY EXISTING MIGRATIONS

Got it?

Cool.

Let's begin

Create an app with some migrations

1. Create a new rails app. Make sure to use postgres. You got this one.

2. Add some models

> rails g model recipe name:string instructions:string posted:string
> rails g model ingredient name:string amount:string

1. Create a relationship between these models using the has_and_belongs_to_many shorthand.

> rails g migration create_join_table_ingredients_recipes ingredients recipes

1. Migrate!

2. Add the relationship in your models:

# models/ingredient.rb
class Ingredient < ActiveRecord::Base
  has_and_belongs_to_many :recipes
end

# models/recipe.rb
class Recipe < ActiveRecord::Base
  has_and_belongs_to_many :ingredients
end

1. Test out these associations in the rails console.

Exercises

1. Oops! I forgot that I wanted an author attribute on the recipe model. Add this attribute now keeping in mind the #1 rule of migration hell.

2. Now that I'm thinking about it, I actually don't want that author attribute... Sorry. Can you delete this attribute?

3. This is really weird. I really didn't think this was going to happen, but I was thinking... shouldn't instructions actually be called steps? Yeah. That makes more sense to me. Modify this attribute.

4. I just realized that I accidentally made the posted attribute on recipes a string! This should be a datetime, der. Can you help me out to change this datatype?

5. I want a new table. Let's call it comments and make it a 1:n relationship with recipes. K thanks.

6. Blerg I HATE comments. Comments are sooo 2015. Drop that table.