How do I add a new attribute to a migration in Rails 3?

Here's my story: I had something like this set up a while ago.

  create_table(:users) do |t|
  t.database_authenticatable :null => false
  t.r开发者_开发知识库ecoverable
  t.rememberable
  t.trackable

  t.integer :total_pageviews

and "total_pageviews" worked fine. I could set it to zero, increment it, multiply it, call it, whatever. but let's say i want to add:

  t.integer :total_votes

What do I have to do to configure total_votes as an attribute? Whenever I try to use "total_votes", I get undefined method error. I'm thinking that the answer is something like rake db:migrate or similar.

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You should not ever alter existing migrations. If you have checked them in to your version control system and somebody else runs them and then you add a new field to them and commit that change, they will not know to get that change. Then you must tell them and it's a pain in the butt to fix.

If you've not committed it yet then rollback the migration (rake db:rollback), make the necessary modification and re-run it again (rake db:migrate).

But in the Real World, you would create a new migration which adds this field using rails g migration add_total_votes_to_users total_votes:integer.

Rails will interpret this migration name and know what to do with it, generating a migration that contains this line:

add_column :users, :total_votes, :integer

Then when you run this migration it will add this total_votes field to the users table which will make an attribute of the same name for all User objects.

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Are you adding this after the migration has been run? So, the users table exists and you want to add a column to it? If so, you need go create a migration like

rails generate migration add_total_votes_to_users 

Open it up (just to verify that the table and column are correct). Then run the migration.

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If you app is in production, then you should create a new migration. If you app is in pre-production stage, and you have a small development team with good communication, then I recommend you to go ahead and modify the migration and then do

rake db:drop
rake db:create
rake db:migrate

then you can commit the modified migration file and let the rest of you team know that that you have changed a migration file.