ROM::SQL

RDBMS suport for Ruby Object Mapper.

Installation

Add this line to your application's Gemfile:

gem 'rom-sql'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rom-sql

Setup

ROM uses Sequel under the hood and exposes its Dataset API in relation objects. For schema migrations you can use its Migration API which is available via repositories.

setup = ROM.setup(sqlite: "sqlite::memory")

setup.sqlite.connection.create_table(:users) do
  primary_key :id
  String :name
  Boolean :admin
end

setup.sqlite.connection.create_table(:tasks) do
  primary_key :id
  Integer :user_id
  String :title
end

Relations

setup.relation(:tasks)

setup.relation(:users) do
  def by_name(name)
    where(name: name)
  end
end

rom = setup.finalize

users = rom.relations.users
tasks = rom.relations.tasks

users.insert(id: 1, name: "Piotr")
tasks.insert(user_id: 1, title: "Be happy")

puts users.by_name("Piotr").with_tasks.to_a.inspect
# => [{:id=>1, :name=>"Piotr", :user_id=>1, :title=>"Be happy"}]

Mapping joins to aggregates

ROM doesn't have a relationship concept like in ActiveRecord or Sequel. Instead it provides a convenient interface for building joined relations that can be mapped to aggregate objects.

There's no lazy-loading, eager-loading or any other magic happening behind the scenes. You're in full control of how data are fetched from the database and it's an explicit operation.

Sequel's association DSL is available in relation definitions which enables association_join interface inside relations. To map joined results to aggregate objects wrap and group mapping transformation can be used

setup.relation(:tasks)

setup.relation(:users) do
  one_to_many :tasks, key: :user_id

  def by_name(name)
    where(name: name)
  end

  def with_tasks
    association_join(:tasks, select: [:title])
  end
end

setup.mappers do
  define(:users) do
    model name: 'User'

    group tasks: [:title]
  end
end

rom = setup.finalize

users = rom.relations.users
tasks = rom.relations.tasks

users.insert(id: 1, name: "Piotr")
tasks.insert(user_id: 1, title: "Be happy")

rom.read(:users).with_tasks.by_name("Piotr").to_a
# => [#<User:0x007fb31542a098 @id=1, @name="Piotr", @tasks=[{:title=>"Be happy"}]>]

ROADMAP

On a very high level:

• Make it dead simple to join relations and support all types of joins
• Make it dead simple to select and alias column names
• Discover conventions for typical query scenarios and make common things trivial, less common things simple and super rare cases possible
• Make mapper interface smart enough to figure out when columns are aliased

For details please refer to issues.

License

See LICENSE file.