A sample ActiveRecord database setup, for inclusion in a test helper, or something

sample_app.rb

require 'active_record'

# A sample application, consisting of products, users, comments, categories, and whatnot.
module SampleApp
  class Product < ActiveRecord::Base
    belongs_to :user
    has_many :comments, :as => :commentable
    has_many :transactions
    has_and_belongs_to_many :categories

    def category_names
      categories.map(&:name)
    end
  end

  class User < ActiveRecord::Base
    has_many :wares,      :class_name => "Product"
    has_many :purchases,  :class_name => "Transaction", :foreign_key => :buyer_id
    has_many :sales,      :through => :wares, :source => :transactions
    has_many :purchased_items, :through => :purchases, :source => :product
    has_many :sold_items, :through => :sales, :source => :product
  end

  class Transaction < ActiveRecord::Base
    belongs_to :product
    belongs_to :buyer,  :class_name => "User"
    has_many :comments, :as => :commentable
  end

  class Comment < ActiveRecord::Base
    belongs_to :user
    belongs_to :commentable, :polymorphic => true
  end

  class Category < ActiveRecord::Base
    has_and_belongs_to_many :products
  end

  def create_connection
    ActiveRecord::Base.establish_connection :adapter => "sqlite3", :database => ":memory:"
  end

  def create_tables
    ActiveRecord::Base.connection.create_table(:products, :force => true) do |t|
      t.string :name
      t.integer :quantity
      t.float :price
      t.integer :user_id
      t.timestamps
    end

    ActiveRecord::Base.connection.create_table(:users, :force => true) do |t|
      t.string :name
      t.timestamps
    end

    ActiveRecord::Base.connection.create_table(:transactions, :force => true) do |t|
      t.integer :buyer_id
      t.integer :product_id
      t.timestamps
    end

    ActiveRecord::Base.connection.create_table(:comments, :force => true) do |t|
      t.string :comment
      t.integer :user_id
      t.integer :commentable_id
      t.integer :commentable_type
      t.timestamps
    end

    ActiveRecord::Base.connection.create_table(:categories, :force => true) do |t|
      t.string :name
      t.timestamps
    end

    ActiveRecord::Base.connection.create_table(:categories_products, :force => true, :id => false) do |t|
      t.integer :category_id
      t.integer :product_id
    end

    ActiveRecord::Base.connection.create_table(:leftovers, :force => true) do |t|
      t.string :blah
    end

    ActiveRecord::Base.connection.create_table(:schema_migrations, :force => true) do |t|
      t.string :version
    end
  end

  def create_records
    @alice = User.create!(:name => 'Alice')
    @anorak = @alice.wares.create!(:name => 'Anorak', :quantity => 1, :price => 9.99)
    @belt = @alice.wares.create!(:name => 'Belt', :quantity => 2, :price => 4.99)
    @cap = @alice.wares.create!(:name => 'Cap', :quantity => 3, :price => 3)
    @anorak.categories << Category.find_or_create_by_name('Clothing')
    @belt.categories << Category.find_or_create_by_name('Clothing')
    @cap.categories << Category.find_or_create_by_name('Clothing')

    @bob = User.create!(:name => 'Bob')
    @alpha = @bob.wares.create!(:name => 'Alpha Romeo', :quantity => 1, :price => 80000)
    @bmw = @bob.wares.create!(:name => 'BMW', :quantity => 1, :price => 60000)
    @chevy = @bob.wares.create!(:name => 'Chevrolet', :quantity => 2, :price => 59999.99)
    @alpha.categories << Category.find_or_create_by_name('Automotive')
    @bmw.categories << Category.find_or_create_by_name('Automotive')
    @chevy.categories << Category.find_or_create_by_name('Automotive')

    @charlie = User.create(:name => 'Charlie')

    @transaction = Transaction.create!(:buyer => @charlie, :product => @anorak)
    @transaction.comments.create!(:user => @charlie, :comment => 'This will keep me dry.')

    @alpha.comments.create!(:user => @charlie, :comment => 'I wish I could afford this.')
  end

  def prepare_database
    create_connection
    create_tables
    create_records
  end
end