using Arrays in Rails with PostgreSQL

migration

class AddSubjectsToBook < ActiveRecord::Migration
  def change
    add_column :books, :subjects, :text, array:true, default: []
  end
end

Querying

2.1.2 :026 > Book.where("'history' = ANY (subjects)")
  Book Load (0.5ms)  SELECT "books".* FROM "books" WHERE ('history' = ANY (subjects))
 => #<ActiveRecord::Relation [#<Book id: "39abef75-56af-4ad5-8065-6b4d58729ee0", title: nil, created_at: "2014-10-17 08:21:17", updated_at: "2014-10-17 19:21:25", description: {}, metadata: {}, subjects: ["education", "business", "history", "finances"]>]>
 
 2.1.2 :027 > Book.where("subjects @> ?", '{finances}')
  Book Load (0.5ms)  SELECT "books".* FROM "books" WHERE (subjects @> '{finances}')
 => #<ActiveRecord::Relation [#<Book id: "39abef75-56af-4ad5-8065-6b4d58729ee0", title: nil, created_at: "2014-10-17 08:21:17", updated_at: "2014-10-17 19:21:25", description: {}, metadata: {}, subjects: ["education", "business", "history", "finances"]>]>

rake

rails g migration add_subjects_to_book subjects:text