RQL

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

Api Documentation

Installation

Add this line to your application's Gemfile:

gem 'rql'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rql

Usage

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

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

Preloading/Eager-Loading

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.

Query DSL

Operators

Operator	Example	SQL (In Postgres)
==	Book.rql.where {pages == 200}	SELECT * FROM "book" WHERE "book"."pages" = 200
!=	Book.rql.where {pages != 200}	SELECT * FROM "book" WHERE "book"."pages" != 200
===	Book.rql.where {pages === (200..300)}	SELECT * FROM "book" WHERE "book"."pages" >= 200 AND "book"."pages" >= 200
>	Book.rql.where {pages > 200}	SELECT * FROM "book" WHERE "book"."pages" > 200
<	Book.rql.where {pages < 200}	SELECT * FROM "book" WHERE "book"."pages" < 200
>=	Book.rql.where {pages >= 200}	SELECT * FROM "book" WHERE "book"."pages" >= 200
<=	Book.rql.where {pages <= 200}	SELECT * FROM "book" WHERE "book"."pages" <= 200
+	Book.rql.where {pages + 2 == 200}	SELECT * FROM "book" WHERE ("book"."pages" + 2) = 200
-	Book.rql.where {pages - 2 == 200}	SELECT * FROM "book" WHERE ("book"."pages" - 2) = 200
*	Book.rql.where {pages * 2 == 200}	SELECT * FROM "book" WHERE "book"."pages" * 2 = 200
/	Book.rql.where {pages / 2 == 200}	SELECT * FROM "book" WHERE "book"."pages" / 2 = 200
\		`Book.rql.where == 200) \
&	Book.rql.where {(pages == 200) & (pages == 300)	SELECT * FROM "book" WHERE "book"."pages" = 200 AND "book"."pages" = 300

Functions

Function	Example	SQL (In Postgres)
start_with?	Book.rql.where namename.start_with?('A')	SELECT * FROM "book" WHERE "book"."name" ILIKE 'A%'
end_with?	Book.rql.where namename.end_with?('A')	SELECT * FROM "book" WHERE "book"."name" ILIKE '%A'
include?	Book.rql.where namename.include?('A')	SELECT * FROM "book" WHERE "book"."name" ILIKE '%A%'
in?	Book.rql.where 'B'])	SELECT * FROM "book" WHERE "book"."name" IN ('A', 'B')

Aggregates	Example
calculate(attribute, operation)	Author.rql.where :sum) > 500
sum(attribute)	Author.rql.where > 500
average(attribute)	Author.rql.where > 250
minimum(attribute)	Author.rql.where > 300
maximum(attribute)	Author.rql.where > 200
count(attribute)	Author.rql.where > 5
count	Author.rql.where > 5

Order

Order	Example	SQL (In Postgres)
asc	Book.rql.order namename.asc	SELECT * FROM "book" ORDER BY "book"."name" ASC
desc	Book.rql.order namename.desc	SELECT * FROM "book" ORDER BY "book"."name" DESC
asc(flag)	Book.rql.order namename.asc(false)	SELECT * FROM "book" ORDER BY "book"."name" DESC
desc(flag)	Book.rql.order namename.desc(false)	SELECT * FROM "book" ORDER BY "book"."name" ASC

Development

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.

Contributing

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.

License

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