Alter Schema in Rails 2

Question

I need to add some columns to a table in my schema. Can someone tell me the best way to do this?

The following seems incomplete or wrong since the schema.rb file did not update to include the new column and all of the corresponding view files (edit,index,new,show) did not update to include the new column. Not to mention the bloat of all of those migration classes that get generated. Thanks

ruby script/generate migration RecordLabelToAlbums record_label:string
      exists  db/migrate
      create  db/migrate/20121130125859_record_label_to_albums.rb

Creates this:

class RecordLabelToAlbums < ActiveRecord::Migration
def self.up
end

def self.down
 end
end

I then added this:

class RecordLabelToAlbums < ActiveRecord::Migration
def self.up
   add_column :albums, :record_label, :text
end

def self.down
   remove_column :albums, :record_label
end

end

The I ran:

rake db:migrate

Got This: Mysql::Error: Table 'albums' already exists: CREATE TABLE albums (id int(11) DEFAULT NULL auto_increment PRIMARY KEY, created_at datetime, updated_at datetime)

Did you run the migration with `rake db:migrate`? You'll need to modify the application code yourself. — Chowlett, Nov 30 '12 at 13:20
Yes, when I started development, I ran rake db:migrate. Now I need to add a few columns to a table and was curious about the best way to do this — Slinky, Nov 30 '12 at 13:28

Tom Harrison · Accepted Answer · 2012-11-30T14:24:12.283

The code you added is correct.

The error suggests that for some reason your system appears to think it has not yet run the original migration that created the albums table. The state of migrations (in Rails 2) is specified in a table in the database called schema_migrations -- if this gets confused then it will try to re-run migrations. I am not sure what might cause it to get confused, but I do recall this happened a couple times back in 2008 when I was using Rails 2.x.

The table is simple -- you can see what's in it from a SQL prompt -- just the names of migrations it thinks it has run, I think.

If you don't mind losing some data, you can try rake db:rollback or even rake db:reset to get back to the beginning. rake db:rollback STEP=2 will rollback the last 2 migrations.

If you need the data, correct the contents of the table by adding one or more new records referencing the migrations in app/db/migrations that may have been missed. The order is important, I think (the format changed a little in Rails 3, I don't recall how).

Any time you want to add or change the database schema, use rails to generate a migration, and then run rake db:migrate once it's ready to go.

And just asking: is there any way you can move to Rails 3. It's been out for years now, and Rails 4 is coming soon. You'll find yourself in a backwater of incompatibilities, deprecations, security and performance issues and so on if you don't take the hit and upgrade.

Thanks, Tom, for your detailed explanation. I inherited this project which from time to time needs to be updated. Is there a good migration guide from Rails 2 to 3? Cheers — Slinky, Nov 30 '12 at 15:03
There are tons. Google "migrating from rails 2 to 3" -- the RailsCasts are good, and it looks like there's a gem to help you figure out what might need to move. (A slight rant to follow: many applications are left in the state you describe. When resources are not allocated to keep the app updated, various security and other issues are left unresolved. It's really a duty of a company to stay relatively current.) Ok, now that I have that off my chest, I feel better :-) — Tom Harrison, Nov 30 '12 at 15:12

Alter Schema in Rails 2

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