Kotauror/ruby_postgres_magic.md

## ruby_postgres_magic.md

      
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              ruby_postgres_magic.md
            
          
    Ruby + Postgresql - understanding the magic.

This is my early attempt at understanding the magic which makes my ruby app work and connect to postgresql database.
Program at the moment:

CONTROLLER :

app.rb
require 'sinatra/base'
require './lib/link'
require './database_connection_setup'

class BookmarkManager < Sinatra::Base
  get "/" do
    @links = Link.all
    erb(:index)
  end

  get '/getlink' do
    erb(:getlink)
  end

  post "/url" do
    Link.create(url: params[:url])
    redirect("/")
  end

  run! if app_file == $0
end
MODEL :

database_connection.rb
class DatabaseConnection
  def self.setup(database_name)
    @connection = PG.connect(dbname: database_name)
  end

  def self.query(sql)
   @connection.exec(sql)
  end
end
database_connection_setup.rb
require './lib/database_connection'

if ENV['ENVIRONMENT'] == 'test'
  DatabaseConnection.setup('bookmark_manager_test')
else
  DatabaseConnection.setup('bookmark_manager')
end
link.rb
require 'pg'
require_relative 'database_connection'

class Link
  def self.all
    result = DatabaseConnection.query("SELECT * FROM links")
    result.map { |link| link['url'] }
  end

  def self.create(hash)
    DatabaseConnection.query("INSERT INTO links (url) VALUES('#{hash[:url]}')")
  end
end
VIEWS :

index.erb:
<html>
  <head></head>
  <body>
    <form action="/getlink" method="get">
      <input type="submit" value="Add link">
    </form>
    <div>
      <ul>
        <% @links.each do |link| %>
          <li>
            <%= link %>
          </li>
        <% end %>
      </ul>
    </div>
  </body>
</html>
getlink.erb:
<form action="/url" method="post">
  <input type="text" name="url" placeholder="Enter URL here">
  <input type="submit" value="Add link">
</form>
OTHER RELEVANT (for this note) FILES

config.ru
require_relative "./app"
run BookmarkManager
spec_helper.rb
ENV['ENVIRONMENT'] = 'test'

require File.join(File.dirname(__FILE__), '..', 'app.rb')
require 'capybara'
require 'capybara/rspec'
require 'rspec'

Capybara.app = BookmarkManager

RSpec.configure do |config|

  config.before(:each) do
    require_relative './test_database_setup'
  end

  config.expect_with :rspec do |expectations|
    expectations.include_chain_clauses_in_custom_matcher_descriptions = true
  end

  config.mock_with :rspec do |mocks|
    mocks.verify_partial_doubles = true
  end

  config.shared_context_metadata_behavior = :apply_to_host_groups

end
test_database_setup.rb
require 'pg'

connection = PG.connect(dbname: 'bookmark_manager_test')

connection.exec("TRUNCATE links;")
connection.exec("INSERT INTO links VALUES(1, 'http://www.makersacademy.com');")
connection.exec("INSERT INTO links VALUES(2, 'http://www.google.com');")
connection.exec("INSERT INTO links VALUES(3, 'http://www.facebook.com');")
How does it work - step by step:

--> when we run rspec


We run rspec
Because of running rspec, spec_helper.rb will be run as well.
spec_helper.rb sets the ENV[ENVIRONMENT] to "test".

then (next line of code in spec_helper), spec_helper.rb loads app.rb.

once the app.rb file is loaded, is will load all the files it requires, including database_connection_setup.rb

database_connection_setup.rb, knowing we're in the test environment, will connect us to the bookmark_manager_test database.


additionally, the spec_helper requires ./test_database_setup to be loaded before each test.

./test_database_setup seeds our test database with links.


--> when we run rackup


First, config.ru file will be run and it will run our app.rb file.
once the app.rb file is loaded, is will load all the files it requires, including database_connection_setup.rb
database_connection_setup.rb will connect us to the bookmark_manager database, which is a database for a non-test environment.

we're not in the test environment because we didn't run spec_helper.rb and so we didn't set our environment to test.