QueryRelation

Provides an ActiveRecord::Relation-like DSL to non-SQL backends

Installation

Add this line to your application's Gemfile:

gem 'query_relation'

And then execute:

$ bundle

Or install it yourself as:

$ gem install query_relation

Usage

The QueryRelation class is provided to encapsulate building a relation. It is a chainable interface, upon which query methods can be called, and final execution is delayed until the last possible moment. It can be instantiated directly, but the more common way to get access to one is to mixin the QueryRelation::Queryable module into your collection.

QueryRelation::Queryable expects a method named search to be implemented by the mixee. search should be written to take two parameters

mode: one of first, last, or all
options: a Hash containing the choices that were made by the caller. It will contain the keys :where, :select, :limit, :offset, :order, group, :includes, and/or :references

The search method should be written to process this set of options and return an Array of the selection. It can use the options and mode in any way it sees fit to optimally return the requested values.

Example

Here's a simple example that supports limit and offset over a simple collection to give an idea of how one might write a search method.

class MyCollection
  include QueryRelation::Queryable

  private

  THE_COLLECTION = [1, 2, 3, 4].freeze

  def search(mode, options)
    collection = filter_collection_by_options(options)

    case mode
    when :first then collection.first
    when :last  then collection.last
    when :all   then collection
    end
  end

  def filter_collection_by_options(options)
    collection = THE_COLLECTION
    collection = collection.drop(options[:offset]) if options[:offset]
    collection = collection.take(options[:limit]) if options[:limit]
    collection
  end
end

MyCollection.new.all.to_a
# => [1, 2, 3, 4]
MyCollection.new.limit(2).to_a
# => [1, 2]
MyCollection.new.limit(1).offset(2).to_a
# => [3]
MyCollection.new.first
# => 1
MyCollection.new.last
# => 4

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/ManageIQ/query_relation. 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 Apache License 2.0.