Question

I am getting to grips with DataMapper on sqlite3 at the moment. I have to models defined which are creating two tables: “companies” and “apps”.

Each app belongs to a company and each company many apps. I want to represent this relationship in my models but I add the “has n” and “belongs_to” methods to each class, the App class stops working when call #create on a bunch of apps, they are not inserted into the database.

If I don’t have the associations methods then everything works fine.

This is my DataMapper code:

DataMapper::setup(:default, "sqlite3://#{Dir.pwd}/app.db")

class Company
    include DataMapper::Resource

    property :id, Serial
    property :company_name,
    property :company_id, Text, :unique => true

    has n, :apps
end

class App
    include DataMapper::Resource

    property :id, Serial
    property :app_id, Integer
    property :bundle_id, Text
    property :game_name, Text
    property :company_name, Text
    property :created_at, DateTime
    property :rank, Integer

    belongs_to :company
end

DataMapper.finalize.auto_upgrade!

puts 'Database and tables created'

This is the code I am using to populate my tables

companies_in_chart.each do |company|
    @add_company = Company.create(
        :company_name   => company["company_name"],
        :company_id     => company["company_id"]
    )
end
puts "Inserted companies into database"

apps_arr.each do |app|
    @new_app = App.create(
        :app_id         => app["app_id"],
        :bundle_id      => app["bundle_id"],
        :game_name      => app["game_name"],
        :company_name   => app["company_name"],
        :created_at     => app["DateTime"],
        :rank           => app["rank"]
    )
end
puts "Inserted apps into database"

EDIT: New code

#Set up database and apps table
DataMapper::setup(:default, "sqlite3://#{Dir.pwd}/app.db")

class Company
    include DataMapper::Resource

    property :id, Serial
    property :company_name, Text,    :required => true, :lazy => false
    property :company_id, Text,      :required => true, :lazy => false, :unique => true

    has n, :apps
end

class App
    include DataMapper::Resource

    property :id, Serial
    property :app_id, Integer,      :required => true
    property :bundle_id, Text,      :required => true, :lazy => false
    property :game_name, Text,      :required => true, :lazy => false
    property :company_id, Text,     :required => true, :lazy => false
    property :created_at, DateTime
    property :rank, Integer

    belongs_to :company
end

DataMapper.finalize.auto_upgrade!

puts 'Database and tables created'

#Insert apps and companies into database
apps_arr.each do |app|

    # Creates a new company based on app entry if the company does
    # not exist in the companies table
    @add_company = Company.create(
        :company_name   => app["company_name"],
        :company_id     => app["company_id"]
    )

    @add_app = App.create(
        :app_id         => app["app_id"],
        :bundle_id      => app["bundle_id"],
        :game_name      => app["game_name"],
        :company_id     => app["company_id"],
        :created_at     => app["DateTime"],
        :rank           => app["rank"]
    )
end
puts "Inserted app and companies into database"

@company = Company.first
ap @company # => #<Company @id=1 @company_name="Rovio Entertainment Ltd" @company_id="rovio">

ap @company.apps # => [] --I was hoping it would return all of Rovio's apps in the database

Answer 1

apps not created cause you have to attach a company when creating app.

if you want to add apps not attached to any company, use this in you App model:

belongs_to :company, :required => false

to attach a company when creating app:

#Insert apps and companies into database

apps_arr.each do |app|

  # Creates a new company based on app entry if the company does
  # not exist in the companies table

  company = Company.first_or_create(
    :company_name   => app["company_name"],
    :company_id     => app["company_id"]
  )

  app = App.first_or_create(
    :company        => company, # you missed this
    :app_id         => app["app_id"],
    :bundle_id      => app["bundle_id"],
    :game_name      => app["game_name"],
    :company_id     => app["company_id"],
    :created_at     => app["DateTime"],
    :rank           => app["rank"]
  )
end
puts "Inserted app and companies into database"

I successfully replicated your code on CIBox and it runs perfectly.

See the code and live demo here

As you can see, it creates a company and attach it to created app.

Company.first.apps returns created app, so associations works correctly.