RQL

RQL is a DSL for Ruby on Rails' ActiveRecord, designed to allow derived/calculated attributes on models to be used in database queries.

Api Documentation

Add this line to your application's Gemfile:

gem 'rql'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rql

Define a derived attribute in your model:

class Book < ActiveRecord::Base
  include Rql::Queryable

  derived_attr :leaves do
    pages / 2
  end
end

then use it in a query:

Book.rql.where(leaves: 100)

or using the dsl

Book.rql.where{leaves > 100}

Aggregate functions can be used in derived attributes:

class Author < ActiveRecord::Base
  include Rql::Queryable
  
  has_many :books
  
  derive_attr :total_books do
    books.count
  end
  
  derive_attr :total_pages do
    books.sum(:page)
  end
  
  derive_attr :long_books do
    books.rql.where{pages > 300}.count
  end
end

Derived attributes can be preloaded to prevent multiple database calls when deriving attributes that reference associated models. To preload derived attributes:

Authors.derive(:total_books, :total_pages)

If a derived attribute has not been preloaded then the code will be evaluated in the context of the model when it is accessed. For instance calling Book.first.leaves will return pages / 2 just as a normal method would, without having to query the database.

As strings in ruby are case sensitive, to get consistent results when derived attributes are both run is the context of model and in the database you will need to configure your database to be case sensitive.

To perform case-insensitive queries downcase the values you are comparing e.g.

Authors.where{name.downcase == my_string.downcase}

Alternatively you can use regexp matching with the =~ operator. This is case sensitive by default but supports the case insensitive flag.

Case sensitive regexp match:

Authors.where{name =~ /[A-Za-z]/}

Case insensitive match using i flag:

Authors.where{name =~ /[A-Z]/i}

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/liefni/rql. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.