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I have a Rails app, where one of the models does not have the id column. Doing some research I found the migration that created it:
create_table(:the_model, :id => false) do |t| # columns end Now, on a new migration, I want to add the id column in a Rails standard way (not using database specific sql). How can I do that?
I already tried this without success:
change_table(:the_model, :id => true) do |t| end 
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Migrations are a feature of Active Record that allows you to evolve your database schema over time. Rather than write schema modifications in pure SQL, migrations allow you to use a Ruby DSL to describe changes to your tables.
Active Record tracks which migrations have already been run so all you have to do is update your source and run rake db:migrate. Active Record will work out which migrations should be run. It will also update your db/schema. rb file to match the structure of your database.
A migration means that you move from the current version to a newer version (as is said in the first answer). Using rake db:migrate you can apply any new changes to your schema. But if you want to rollback to a previous migration you can use rake db:rollback to nullify your new changes if they are incorrectly defined.
You can either manually add the id column:
add_column :table_name, :id, :primary_key or clear (or backup) your data, rollback to this migration, get rid of the option :id => false, and re-migrate.
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