Ransack: How to use existing scope?

Question

Converting a Rails 2 application to Rails 3, I have to replace the gem searchlogic. Now, using Rails 3.2.8 with the gem Ransack I want to build a search form which uses an existing scope. Example:

class Post < ActiveRecord::Base
  scope :year, lambda { |year| 
    where("posts.date BETWEEN '#{year}-01-01' AND '#{year}-12-31'") 
  }
end  

So far as I know, this can be achieved by defining a custom ransacker. Sadly, I don't find any documentation about this. I tried this in the Postclass:

ransacker :year, 
          :formatter => proc {|v| 
            year(v)
          }

But this does not work:

Post.ransack(:year_eq => 2012).result.to_sql
=> TypeError: Cannot visit ActiveRecord::Relation

I tried some variations of the ransacker declaration, but none of them work. I Need some help...

UPDATE: The scope above is just on example. I'm looking for a way to use every single existing scope within Ransack. In MetaSearch, the predecessor of Ransack, there is a feature called search_methods for using scopes. Ransack has no support for this out of the box yet.

Answer 1

ransack supports it out of the box after merging https://github.com/activerecord-hackery/ransack/pull/390 . you should declare ransakable_scopes method to add scopes visible for ransack.

From manual

Continuing on from the preceding section, searching by scopes requires defining a whitelist of ransackable_scopes on the model class. The whitelist should be an array of symbols. By default, all class methods (e.g. scopes) are ignored. Scopes will be applied for matching true values, or for given values if the scope accepts a value:

class Employee < ActiveRecord::Base
  scope :activated, ->(boolean = true) { where(active: boolean) }
  scope :salary_gt, ->(amount) { where('salary > ?', amount) }

  # Scopes are just syntactical sugar for class methods, which may also be used:

  def self.hired_since(date)
    where('start_date >= ?', date)
  end

  private

  def self.ransackable_scopes(auth_object = nil)
    if auth_object.try(:admin?)
      # allow admin users access to all three methods
      %i(activated hired_since salary_gt)
    else
      # allow other users to search on `activated` and `hired_since` only
      %i(activated hired_since)
    end
  end
end

Employee.ransack({ activated: true, hired_since: '2013-01-01' })

Employee.ransack({ salary_gt: 100_000 }, { auth_object: current_user })