```ruby
class AddPreferencesCountToStudents < ActiveRecord::Migration
  def change
  	add_column :students, :preferences_count, :integer
  end
end
```

Set preferences_count default to 0
user
```ruby
class AddPreferencesCountToStudents < ActiveRecord::Migration
  def change
  	add_column :students, :preferences_count, :integer, default: 0
  end
end
```
assistant