Question

I generated a new rails migration:

rails generate migration some_new_column_to_table

edit: —

ran the migration:

rake db:migrate

updated test db:

rake db:test:prepare

realized I hadn’t added anything to the change method, then

updated the migration file:

class AddSomeColumnToTable < ActiveRecord::Migration
  def change
    add_column :table, :some_column, :string
    add_index :table, :some_column
  end
end

ran the migration (again):

rake db:migrate

updated test db (again):

rake db:test:prepare

After running these commands “some_column” had not be added to the database. I found a solution to this problem here: rake db:migrate is not working

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

Why did this fix the problem?
How can I prevent it in the future?

Answer 1

It’s not clear what your problem is. But your last commands do straighten things out.

rake db:drop:all  << drop the database
rake db:create:all  << create the database (not the tables)
rake db:migrate << build up the database based on the migrations

In my experience, migrations don’t ‘stop working’ and they do exactly as layed out, as they are no more than individual commands. But, they require their execution to be done in order, so if you start editing the migrations, you have to be aware of whether a migration has run or not. Migration problems are typically the result of our editing them out-of-sequence. The safest best is to don’t edit migrations that have run already. First do any of the following:

rake db:rollback  << rollback the last migration (you can do this multiple times)
rake db:migrate VERSION=00000   << This will rollback to a specific migration
rake db:rollback STEP=2 << rollback 2 migrations

Hopefully that’s helpful.