```ruby
require 'active_record'
require 'exercism/use_cases/updates_user_exercise'

class UserExercise < ActiveRecord::Base
  has_many :submissions
end

class Submission < ActiveRecord::Base
  belongs_to :user_exercise
end

namespace :migrate do
  desc "migrate user exercise data"
  task :user_exercises do
    require 'db/connection'
    DB::Connection.establish

    sql = "SELECT DISTINCT user_id, language, slug FROM submissions s LEFT JOIN user_exercises e ON s.user_exercise_id=e.id WHERE e.id IS NULL"
    sql = "SELECT DISTINCT user_id, language, slug FROM submissions"
    ActiveRecord::Base.connection.execute(sql).each do |result|
      begin
        Hack::UpdatesUserExercise.new(result["user_id"], result["language"], result["slug"]).update
        print "."
      rescue => e
        puts
        puts e.message
      end
    end
    puts
  end
end

```

Optimize user exercise data migration
user
```ruby
require 'active_record'
require 'exercism/use_cases/updates_user_exercise'

class UserExercise < ActiveRecord::Base
  has_many :submissions
end

class Submission < ActiveRecord::Base
  belongs_to :user_exercise
end

namespace :migrate do
  desc "migrate user exercise data"
  task :user_exercises do
    require 'db/connection'
    DB::Connection.establish

    sql = "SELECT DISTINCT user_id, language, slug FROM submissions s LEFT JOIN user_exercises e ON s.user_exercise_id=e.id WHERE e.id IS NULL"
    ActiveRecord::Base.connection.execute(sql).each do |result|
      begin
        Hack::UpdatesUserExercise.new(result["user_id"], result["language"], result["slug"]).update
        print "."
      rescue => e
        puts
        puts e.message
      end
    end
    puts
  end
end

```
assistant