```ruby
class AddCategories < ActiveRecord::Migration
  def change
     add_column :nodes, :name, :string
     add_column :nodes, :lft, :integer
     add_column :nodes, :rgt, :integer
     add_column :nodes, :depth, :integer
  end
end
```

Remove rgt and lft from categories
user
```ruby
class AddCategories < ActiveRecord::Migration
  def self.up
    # add_column :nodes, :name, :string
    # add_column :nodes, :lft, :integer
    # add_column :nodes, :rgt, :integer
    # add_column :nodes, :depth, :integer
  end

  def self.down
    # remove_column :nodes, :name
    # remove_column :nodes, :lft
    # remove_column :nodes, :rgt
    # remove_column :nodes, :depth
  end
end
```
assistant