Question

I’m using Heroku to host my Ruby on Rails application and for one reason or another, I may have some duplicate rows.

Is there a way to delete duplicate records based on 2 or more criteria but keep just 1 record of that duplicate collection?

In my use case, I have a Make and Model relationship for cars in my database.

Make      Model
---       ---
Name      Name
          Year
          Trim
          MakeId

I’d like to delete all Model records that have the same Name, Year and Trim but keep 1 of those records (meaning, I need the record but only once). I’m using Heroku console so I can run some active record queries easily.

Any suggestions?

Answer 1

class Model

  def self.dedupe
    # find all models and group them on keys which should be common
    grouped = all.group_by{|model| [model.name,model.year,model.trim,model.make_id] }
    grouped.values.each do |duplicates|
      # the first one we want to keep right?
      first_one = duplicates.shift # or pop for last one
      # if there are any more left, they are duplicates
      # so delete all of them
      duplicates.each{|double| double.destroy} # duplicates can now be destroyed
    end
  end

end

Model.dedupe

• Find All
• Group them on keys which you need for uniqueness
• Loop on the grouped model’s values of the hash
• remove the first value because you want to retain one copy
• delete the rest