nwimmer123/breweries_models_and_migrations

A lab on models and migrations

Active Record Migrations and Associations Lab - Backend Breweries

We're going to build a beer app.

More specifically we want to keep track of the beers brewed by various brewing companies. We'll be skipping the front-end code and focusing solely on things tied to the database.
This lab will force you to write and run several migrations so you get experience doing so.

Objectives
Add columns to the database using database migrations
Remove columns from the database using migrations
Create associations between two models
Write a migration to add foreign keys to tables

Introduction

Our system is going to track two types of data.

1. breweries
2. beers (varieties of beers)

This means we'll have two models and a relationship between them. We'll determine specific column names as we move forward.

Committing

Every time you make a change that is atomic, commit your changes. We should be able to see at least 1 commit for each step in the lab.

Step 1 - The first model

The first model we'll create is the beer model. Use the rails g model command to create a new model beer and migration with columns:

• name
• abv

Determine appropriate data-types for these columns.

spoiler

`> rails g model beer name:string abv:decimal`

# db/migrate/20160111190152_create_beers.rb
class CreateBeers < ActiveRecord::Migration
  def change
    create_table :beers do |t|
      t.string :name
      t.decimal :abv

      t.timestamps null: false
    end
  end
end

# app/models/beer.rb
class Beer < ActiveRecord::Base
end

Verify your changes and then run rake db:create db:migrate.

Note that you can chain rake commands on one-line.

As always commit your changes. (It should be 3 files.) For all steps, feel free to commit after testing your change.

Test your changes in the console

Run rails c or rails console

In the console play around and save a few beers (at least 3). Use commands like:

• Beer.all
• Beer.new
• Beer.create
• Beer.destroy_all
• Beer.find
• Beer.find_by_xxxxxx
• #save

Example:

Running via Spring preloader in process 7845
Loading development environment (Rails 4.2.4)
irb(main):001:0> Beer.all
  Beer Load (0.3ms)  SELECT "beers".* FROM "beers"
=> #<ActiveRecord::Relation []>
irb(main):002:0> od = Beer.new(name: "Original Dankster", abv: 8.2)
=> #<Beer id: nil, name: "Original Dankster", abv: #<BigDecimal:7fa82d9a6b90,'0.82E1',18(36)>, created_at: nil, updated_at: nil>
irb(main):003:0> od.save
   (0.2ms)  BEGIN
  SQL (0.3ms)  INSERT INTO "beers" ("name", "abv", "created_at", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id"  [["name", "Original Dankster"], ["abv", "8.2"], ["created_at", "2016-01-11 19:12:29.282974"], ["updated_at", "2016-01-11 19:12:29.282974"]]
   (1.0ms)  COMMIT
=> true
irb(main):004:0> Beer.all
  Beer Load (0.4ms)  SELECT "beers".* FROM "beers"
=> #<ActiveRecord::Relation [#<Beer id: 2, name: "Original Dankster", abv: #<BigDecimal:7fa82d974f28,'0.82E1',18(18)>, created_at: "2016-01-11 19:12:29", updated_at: "2016-01-11 19:12:29">]>
irb(main):005:0> mo = Beer.create(name: "Mo' Simcoe", abv: 6.5)
   (0.2ms)  BEGIN
  SQL (0.3ms)  INSERT INTO "beers" ("name", "abv", "created_at", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id"  [["name", "Mo' Simcoe"], ["abv", "6.5"], ["created_at", "2016-01-11 19:13:35.464834"], ["updated_at", "2016-01-11 19:13:35.464834"]]
   (1.0ms)  COMMIT
=> #<Beer id: 3, name: "Mo' Simcoe", abv: #<BigDecimal:7fa82d95e020,'0.65E1',18(36)>, created_at: "2016-01-11 19:13:35", updated_at: "2016-01-11 19:13:35">
irb(main):006:0> Beer.create(name: "Bangerang", abv: 6.5)
   (0.2ms)  BEGIN
  SQL (0.2ms)  INSERT INTO "beers" ("name", "abv", "created_at", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id"  [["name", "Bangerang"], ["abv", "6.5"], ["created_at", "2016-01-11 19:14:44.839058"], ["updated_at", "2016-01-11 19:14:44.839058"]]
   (1.0ms)  COMMIT
=> #<Beer id: 4, name: "Bangerang", abv: #<BigDecimal:7fa82f113148,'0.65E1',18(36)>, created_at: "2016-01-11 19:14:44", updated_at: "2016-01-11 19:14:44">
irb(main):007:0> Beer.all.count
   (0.5ms)  SELECT COUNT(*) FROM "beers"
=> 3

Step 2 - Adding more columns

Obviously a beer is more than just it's abv and name. Let's track more information.

Write and run a migration to add fields for:

• brewery_name
• short_description (less than 255 chars)
• long_description
• style (e.g. IPA, Porter)

spoiler

`rails g migration AddDescriptionsToBeers brewery_name:string short_description:string long_description:text style:string`

class AddDescriptionsToBeers < ActiveRecord::Migration
  def change
    add_column :beers, :brewery_name, :string
    add_column :beers, :short_description, :string
    add_column :beers, :long_description, :text
    add_column :beers, :style, :string
  end
end

• After creating the migration, what do you need to run?
• What files are changed? Should you commit them?

Test your changes in the console

1. Add a couple new beers and fill in some of the new fields
2. Find and update your previously created beers, add more details.

sample

```console => #, created_at: "2016-01-11 19:13:35", updated_at: "2016-01-11 19:13:35", brewery_name: nil, short_description: nil, long_desc ```

Step 3 - Create the Second Model

Our Second model will be to track brewing companies; let's call it Brewer.

What sort of data would we want to track about brewers? A few possibilities:

• name
• city
• state
• website_url

Feel free to add your own!

Go ahead and make these database changes now.

Test your changes in the console

Enter the rails console and add a couple of brewers. We don't yet have any association with the beers themselves, don't worry about that, we're coming to it soon. For now just create a couple brewers.

sample

``` irb(main):002:0> Brewer.create(name: "Cellarmaker Brewing Co.", city: "San Francisco", state: "CA") (0.1ms) BEGIN SQL (0.4ms) INSERT INTO "brewers" ("name", "city", "state", "created_at", "updated_at") VALUES ($1, $2, $3, $4, $5) RETURNING "id" [["name", "Cellarmaker Brewing Co."], ["city", "San Francisco"], ["state", "CA"], ["created_at", "2016-01-11 19:32:42.792078"], ["updated_at", "2016-01-11 19:32:42.792078"]] (0.4ms) COMMIT => # irb(main):003:0> Brewer.last Brewer Load (0.7ms) SELECT "brewers".* FROM "brewers" ORDER BY "brewers"."id" DESC LIMIT 1 => # ```

Step 4 - 1:N

As you can imagine most brewers produce more than one variety of beer. Also we know that each beer can only be associated with one brewer.

That means we have a 1:N relationship.

Quick quiz

Please complete the following using ActiveRecord terminology.

Fill in the blank
A brewer __________ beers.
A beer _________ a brewer.

• Which table will contain the foreign key?

solution

| A brewer **has_many** beers. | | A beer **belongs_to** a brewer. |

• The beers table will contain a foreign key to tie it to each brewer.

---

Do the following:

1. Write and run a migration to add the foreign_key

• Don't forget about using references or belongs_to

1. Update the rails model files to specify the relationship between beer and brewer.

spoiler

rails g migration AddBrewerReferenceToBeer brewer:references

Isn't this nice:

class AddBrewerReferenceToBeer < ActiveRecord::Migration
  def change
    add_reference :beers, :brewer, index: true, foreign_key: true
  end
end

did you commit? The migration, schema.rb and the two models should all be in one commit. They require each other to continue working.

Test your change in the console

You might start with something easy like: Brewer.last.beers << Beer.last

irb(main):001:0> Brewer.last
  Brewer Load (0.6ms)  SELECT  "brewers".* FROM "brewers"  ORDER BY "brewers"."id" DESC LIMIT 1
=> #<Brewer id: 1, name: "Cellarmaker Brewing Co.", state: "CA", city: "San Francisco", website_url: nil, created_at: "2016-01-11 19:32:42", updated_at: "2016-01-11 19:32:42">
irb(main):002:0> Brewer.last.beers << Beer.last
  Brewer Load (0.5ms)  SELECT  "brewers".* FROM "brewers"  ORDER BY "brewers"."id" DESC LIMIT 1
  Beer Load (0.4ms)  SELECT  "beers".* FROM "beers"  ORDER BY "beers"."id" DESC LIMIT 1
   (0.1ms)  BEGIN
  SQL (0.5ms)  UPDATE "beers" SET "brewer_id" = $1, "updated_at" = $2 WHERE "beers"."id" = $3  [["brewer_id", 1], ["updated_at", "2016-01-11 19:43:26.433293"], ["id", 4]]
   (6.0ms)  COMMIT
  Beer Load (0.2ms)  SELECT "beers".* FROM "beers" WHERE "beers"."brewer_id" = $1  [["brewer_id", 1]]
=> #<ActiveRecord::Associations::CollectionProxy [#<Beer id: 4, name: "Bangerang", abv: #<BigDecimal:7fa82d9c48e8,'0.65E1',18(18)>, created_at: "2016-01-11 19:14:44", updated_at: "2016-01-11 19:43:26", brewery_name: nil, short_description: nil, long_description: nil, style: nil, brewer_id: 1>]>
irb(main):003:0> Brewer.last
  Brewer Load (0.4ms)  SELECT  "brewers".* FROM "brewers"  ORDER BY "brewers"."id" DESC LIMIT 1
=> #<Brewer id: 1, name: "Cellarmaker Brewing Co.", state: "CA", city: "San Francisco", website_url: nil, created_at: "2016-01-11 19:32:42", updated_at: "2016-01-11 19:32:42">
irb(main):004:0> Brewer.last.beers
  Brewer Load (0.5ms)  SELECT  "brewers".* FROM "brewers"  ORDER BY "brewers"."id" DESC LIMIT 1
  Beer Load (0.3ms)  SELECT "beers".* FROM "beers" WHERE "beers"."brewer_id" = $1  [["brewer_id", 1]]
=> #<ActiveRecord::Associations::CollectionProxy [#<Beer id: 4, name: "Bangerang", abv: #<BigDecimal:7fa82f1667f8,'0.65E1',18(18)>, created_at: "2016-01-11 19:14:44", updated_at: "2016-01-11 19:43:26", brewery_name: nil, short_description: nil, long_description: nil, style: nil, brewer_id: 1>]>
irb(main):005:0> Brewer.last.beers.count
  Brewer Load (0.5ms)  SELECT  "brewers".* FROM "brewers"  ORDER BY "brewers"."id" DESC LIMIT 1
   (0.2ms)  SELECT COUNT(*) FROM "beers" WHERE "beers"."brewer_id" = $1  [["brewer_id", 1]]
=> 1

Step 5 - remove the brewery_name column

Since we now have a separate model for the brewer we no longer need a column on the beers table to list the brewery_name.

1. Write and run a migration to remove the unneeded column.
2. Verify your changes in the console.

spoiler

`rails g migration RemoveBrewerNameFromBeer brewery_name:string`

More

On your own do the following:

1. Add more columns to Brewer like year_founded, phone, latitude, longitude, image_url
2. Add more columns to Beer like ibu (international bittering unit), seasonal (true/false) etc
3. Create a new model Review to track reviews for each Beer.

• Associate this table with the Beer table.
• Add a few fake reviews.

Advanced Challenges

1. Delete this app and start over; re-build it from scratch.
2. Create controllers and at least one view to show the above data.