Configurando la Base de Datos en Heroku con DataMapper. Despliegue

Heroku utiliza la base de datos PostgreSQL y una URL en una variable de entorno ENV['DATABASE_URL'].

configure :development, :test do
  DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/development.db")
end

configure :production do
  DataMapper.setup(:default, ENV['DATABASE_URL'])
end

Estas líneas especifican que se usa SQLite en desarrollo y testing y PostgreSQL en producción. Obsérvese que el Gemfile debe estar coherente:

[~/sinatra/sinatra-datamapper-jump-start(master)]$ cat Gemfile
source 'https://rubygems.org'
gem "sinatra"
gem "slim"
gem "sass"
gem "dm-core"
gem "dm-migrations"
gem "thin"
gem "pg", :group => :production
gem "dm-postgres-adapter", :group => :production
gem "dm-sqlite-adapter", :group => [:development, :test]

o mejor:

group :production do
    gem "pg"
    gem "dm-postgres-adapter"
end

group :development, :test do
  gem "dm-sqlite-adapter"
end

Bundle: installing groups. General considerations

By default, bundle install will install all gems in all groups in your Gemfile, except those declared for a different platform^46.1.

However, you can explicitly tell bundler to skip installing certain groups with the --without option. This option takes a space-separated list of groups.

While the --without option will skip installing the gems in the specified groups, it will still download those gems and use them to resolve the dependencies of every gem in your Gemfile.

This is so that installing a different set of groups on another machine (such as a production server) will not change the gems and versions that you have already developed and tested against.

Bundler guarantees that the third-party code you are running in development and testing is also the third-party code you are running in production. You can choose to exclude some of that code in different environments, but you will never be caught flat-footed by different versions of third-party code being used in different environments.

For a simple illustration, consider the following Gemfile:

           source "https://rubygems.org"

           gem "sinatra"

           group :production do
             gem "rack-perftools-profiler"
           end

In this case, sinatra depends on any version of Rack (>= 1.0), while rack-perftools-profiler depends on 1.x (~> 1.0).

When you run bundle install --without production in development, we look at the dependencies of rack-perftools-profiler as well.

That way, you do not spend all your time developing against Rack 2.0, using new APIs unavailable in Rack 1.x, only to have bundler switch to Rack 1.2 when the production group is used.

This should not cause any problems in practice, because bundle does not attempt to install the gems in the excluded groups, and only evaluates them as part of the dependency resolution process.

This also means that you cannot include different versions of the same gem in different groups, because doing so would result in different sets of dependencies used in development and production.

Because of the vagaries of the dependency resolution process, this usually affects more than just the gems you list in your Gemfile, and can (surprisingly) radically change the gems you are using.

Recordando los pasos para el despliegue en Heroku

heroku create ...

git push heroku master

heroku open

heroku logs --source app

Creando/Modificando la base de datos en Heroku con heroku run console

Ahora ejecutamos la consola de heroku:

heroku run console

lo que nos abre una sesión irb.

Ahora creamos la base de datos en Heroku:

[~/sinatra/sinatra-datamapper-jump-start(master)]$ heroku run console
Running `console` attached to terminal... up, run.8011
irb(main):001:0> require './main'
=> true
irb(main):002:0> DataMapper.auto_migrate!
=> #<DataMapper::DescendantSet:0x007fb89c878230 @descendants=#<DataMapper::SubjectSet:0x007fb89c8781b8 @entries=#<DataMapper::OrderedSet:0x007fb89c878190 @cache=#<DataMapper::SubjectSet::NameCache:0x007fb89c878168 @cache={"Song"=>0}>, @entries=[Song]>>>
irb(main):003:0>

Véase también la práctica TicTacToe 33.28 y el capítulo Despliegue en Heroku 52.