OrderAsSpecified

OrderAsSpecified adds the ability to query an ActiveRecord class for results from the database in an arbitrary order, without having to store anything extra in the database.

It's as easy as:

class TestObject
  extend OrderAsSpecified
end

TestObject.order_as_specified(language: ["es", "en", "fr"])
=> #<ActiveRecord::Relation [
     #<TestObject id: 3, language: "es">,
     #<TestObject id: 1, language: "en">,
     #<TestObject id: 4, language: "en">,
     #<TestObject id: 2, language: "fr">
   ]>

Is this like ranked-model?

Other gems like ranked-model, acts_as_sortable, etc. assume you want the same ordering each time, and store data to keep track of this in the database. They're great at what they do, but if you want to change the ordering, or if you don't always want an ordering, this gem is your friend.

Installation

Add this line to your application's Gemfile:

gem 'order_as_specified'

And then execute:

$ bundle

Or install it yourself as:

$ gem install order_as_specified

Usage

Basic usage is simple:

class TestObject
  extend OrderAsSpecified
end

TestObject.order_as_specified(language: ["es", "en", "fr"])
=> #<ActiveRecord::Relation [
     #<TestObject id: 3, language: "es">,
     #<TestObject id: 1, language: "en">,
     #<TestObject id: 4, language: "en">,
     #<TestObject id: 2, language: "fr">
   ]>

This returns all TestObjects in the given language order. Note that this ordering is not possible with a simple ORDER BY. Magic!

Like any other ActiveRecord relation, it can be chained:

TestObject.
  where(language: ["es", "en", "fr"]).
  order_as_specified(language: ["es", "en", "fr"]).
  limit(3)
=> #<ActiveRecord::Relation [
     #<TestObject id: 3, language: "es">,
     #<TestObject id: 1, language: "en">,
     #<TestObject id: 4, language: "en">
   ]>

We can use chaining in this way to order by multiple attributes as well:

TestObject.
  order_as_specified(language: ["es", "en"]).
  order_as_specified(id: [4, 3, 5]).
  order(:updated_at)
=> #<ActiveRecord::Relation [

  # First is language "es"...
     #<TestObject id: 1, language: "es", updated_at: "2016-08-01 02:22:00">,

    # Within the language, we order by :updated_at...
     #<TestObject id: 2, language: "es", updated_at: "2016-08-01 07:29:07">,

  # Then language "en"...
     #<TestObject id: 9, language: "en", updated_at: "2016-08-03 04:11:26">,

    # Within the language, we order by :updated_at...
     #<TestObject id: 8, language: "en", updated_at: "2016-08-04 18:52:14">,

  # Then id 4...
     #<TestObject id: 4, language: "fr", updated_at: "2016-08-01 12:59:33">,

  # Then id 3...
     #<TestObject id: 3, language: "ar", updated_at: "2016-08-02 19:41:44">,

  # Then id 5...
     #<TestObject id: 5, language: "ar", updated_at: "2016-08-02 22:12:52">,

  # Then we order by :updated_at...
     #<TestObject id: 7, language: "fr", updated_at: "2016-08-02 14:27:16">,
     #<TestObject id: 6, language: "ar", updated_at: "2016-08-03 14:26:06">,
   ]>

We can also use this when we want to sort by an attribute in another model:

TestObject.
  joins(:other_object).
  order_as_specified(other_objects: { id: [other1.id, other3.id, other2.id] })

Neat, huh?

In all cases, results with attribute values not in the given list will be sorted as though the attribute is NULL in a typical ORDER BY:

TestObject.order_as_specified(language: ["fr", "es"])
=> #<ActiveRecord::Relation [
     #<TestObject id: 2, language: "fr">,
     #<TestObject id: 3, language: "es">,
     #<TestObject id: 1, language: "en">,
     #<TestObject id: 4, language: "en">
   ]>

The order can also include nil attributes:

TestObject.order_as_specified(language: ["es", nil, "fr"])
=> #<ActiveRecord::Relation [
     #<TestObject id: 3, language: "es">,
     #<TestObject id: 1, language: nil>,
     #<TestObject id: 4, language: nil>,
     #<TestObject id: 2, language: "fr">
   ]>

distinct_on

In databases that support it (such as PostgreSQL), you can also use an option to add a DISTINCT ON to your query when you would otherwise have duplicates:

TestObject.order_as_specified(distinct_on: true, language: ["fr", "en"])
=> #<ActiveRecord::Relation [
     #<TestObject id: 2, language: "fr">,
     #<TestObject id: 3, language: "en">,
     #<TestObject id: 4, language: "es">
   ]>

case_insensitive

If you want objects to come back in an order that is case-insensitive, you can pass the case_insensitive: true value to the order_as_specified call, as in:

TestObject.order_as_specified(case_insensitive: true, language: ["fr", "en"])
=> #<ActiveRecord::Relation [
     #<TestObject language: "fr">
     #<TestObject language: "FR">
     #<TestObject language: "EN">
     #<TestObject language: "en">
   ]>

Limitations

Databases may have limitations on the underlying number of fields you can have in an ORDER BY clause. For example, in PostgreSQL if you pass in more than 1664 list elements you'll receive this error:

PG::ProgramLimitExceeded: ERROR: target lists can have at most 1664 entries

That's a database limitation that this gem cannot avoid, unfortunately.

Documentation

We have documentation on RubyDoc.

Contributing

1. Fork it (https://github.com/panorama-ed/order_as_specified/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Make sure your changes have appropriate tests (bundle exec rspec) and conform to the Rubocop style specified.

License

OrderAsSpecified is released under the MIT License.