Adding Columns to Tables with the Migration Generator
12:11 PM EDT Monday, April 21 2008
I just stumbled upon a neat little Rails feature and figured I'd share with the world. I'm working on a Facebook application and I'm going through some of the examples in Developing Facebook Platform Applications with Rails. In chapter 4, one of the tasks is:
Let's add a boolean hit column to our attack model. I'll wait while you create that migration.
It doesn't tell you how to do that, which I like. This is a simple enough task the reader should be able to do in their own, no need to clutter up the book with the code.
So I set out to do that, but for whatever reason my mind is in a bit of a fog today. I don't what it is, I've been making an inordinate number of typos. So when my fingers went to type the command to generate the migration, I just instinctively did this:
script/generate migration add_hit_to_attack hit:boolean
I accidentally added the hit:boolean column specification as if this were a script/generate model Whatever command. But it turns out Rails is able to read my mind. I opened up the migration file that was generated and there was this:
class AddHitToAttack < ActiveRecord::Migration
def self.up
add_column :attacks, :hit, :boolean
end
def self.down
remove_column :attacks, :hit
end
end
The code to add the column was already there. I checked the docs and sure enough there is support for this naming convention:
You can name your migration in either of these formats to generate add/remove
column lines from supplied attributes: AddColumnsToTable or RemoveColumnsFromTable
Example:
`./script/generate migration AddSslFlag`
With 4 existing migrations, this creates the AddSslFlag migration in
db/migrate/005_add_ssl_flag.rb
`./script/generate migration AddTitleBodyToPost title:string body:text published:boolean`
This will create the AddTitleBodyToPost in db/migrate/005_add_title_body_to_post.rb with
this in the Up migration:
add_column :posts, :title, :string
add_column :posts, :body, :text
add_column :posts, :published, :boolean
And this in the Down migration:
remove_column :posts, :published
remove_column :posts, :body
remove_column :posts, :title
