Ransack - Polymorphic Associations Search Ransacker

model.rb

class MyModel < ActiveRecord::Base
  belongs_to :owner, polymorphic: true

  ransacker :owner_name, formatter: proc { |value|
    # To use this, you have to know what all of the possible owner types can be.
    # For this example, the #owner_type could be either Group or Advertiser.
    # The fields we want to search on are:
    #   Group#name
    #   Advertiser#contact_name
    # 
    # This method does perform one database hit for each related table.
    # This makes sense considering you are searching on each table's data.
    # 
    # First, gather the IDs for MyModel where it matches the Advertiser#contact_name.
    # Using a nested query on the #where conditional for #owner_id eliminates the
    # need for two queries.
    # 
    # Second, gather the IDs for MyModel where it matches Group#name.
    # 
    # Each query will be finished with #pluck, which returns an array - either the IDs,
    # or an empty array.  Each array is joined simply by adding them together.
    # 
    my_model_ids = MyModel.where(
      owner_id: Advertiser.select('advertisers.id as owner_id').where('contact_name LIKE ?', "%#{value}%"),
      owner_type: 'Advertiser'
    ).pluck(:id) + MyModel.where(
      owner_id: Group.select('groups.id as owner_id').where('name LIKE ?', "%#{value}%"),
      owner_type: 'Group'
    ).pluck(:id)

    # Now that there is a list of the appropriate IDs that match the specification,
    # return the array of IDs as the formatted value for the ransacker.
    # #presence is provided by ActiveSupport, which basically is shorthand for:
    # 
    #   my_model_ids.any? ? my_model_ids : nil
    # 
    # If there are no values, it will return nil, which tells Ransack that no
    # records exist.  An empty array may perform other searches unnecessarily.
    my_model_ids.presence
  } do |parent|
    # #parent references the ransacker, and #table references the table for this
    # model (MyModel).  Pass in :id to #table to tell the ransacker the search is
    # based on the ID field.
    parent.table[:id]
  end
end

view.haml

= search_form_for @search do |f|
  # For this search, the #in predicate needs to be used for Ransack to work properly,
  # since, based on the implementation of the ransacker, we are finding IDs IN the
  # current search model.  Other predicates expect one singular return value.
  # 
  # A value needs to manually be specified for the field.  If the search is on
  # "Minnesota", Ransack will output this as "[\"Minnesota\"]" when the page reloads,
  # since it is an "in" predicate search, and, due to its nature, assumes it is an array
  # of values.
  #
  = f.text_field :owner_name_in, value: params.fetch(:q, {}).fetch(:owner_name_in, nil)