Writing complex queries in plain ActiveRecord is sometimes cumbersome. We need to fallback to write SQL-ish queries as plain strings which could cause errors and is not a way we should query using ORM frameworks. However there is very interesting solution for this problem called Squeel. As its GitHub page says Squeel improves ActiveRecord by making the ARel awesomeness that lies beneath Active Record more accessible.

So according to its documentation we can rewrite this:

Article.where ['created_at >= ?', 2.weeks.ago]

into this:

Article.where{created_at >= 2.weeks.ago}

Pretty nice in my opinion.

Now lets look at some more complex example. We have presentations that belongs to conference either via direct relation (conference_id in Presentation model), or through some event (event_id in Presentation and conference_id in Event model). Presentation could also be not yet assigned to any conference. Now we have admin panel with admin users dedicated to manage certain set of conferences and we want to scope presentations on view to only those which belongs to managed conferences, or which aren’t yet assigned to any (BTW if you are using ActiveAdmin you can scope the queries using scope_to). We need proper scope for this task, and one could be easily written using Squeel:

# models/presentation.rb
scope :unassigned_or_assigned_to, ->(conferences) do
  includes(:sessions).where{ (conference_id >> conferences) |
    (events.conference_id >> conferences) |
    ((conference_id == nil) & (events.conference_id == nil)) }
end

Usage of such scope is straightforward:

# models/admin_user.rb
def managed_presentations
  if superadmin?
    Presentation
  else
    Presentation.unassigned_or_assigned_to conferences
  end
end

I’ll definitely consider using Squeel whenever I’ll need to write complex query.