You won't always be able to simply generate the migration to already have the code you want. You can create an empty migration and then populate it with the code you need.

You can find information about how to accomplish different tasks in a migration here:

http://api.rubyonrails.org/classes/ActiveRecord/Migration.html

More specifically, you can see how to drop a table using the following approach:

drop_table :table_name

First generate an empty migration with any name you'd like. It's important to do it this way since it creates the appropriate date.

rails generate migration DropProductsTable

This will generate a .rb file in /db/migrate/ like 20111015185025_drop_products_table.rb

Now edit that file to look like this:

class DropProductsTable < ActiveRecord::Migration  def up    drop_table :products  end  def down    raise ActiveRecord::IrreversibleMigration  endend

The only thing I added was drop_table :products and raise ActiveRecord::IrreversibleMigration.

Then run rake db:migrate and it'll drop the table for you.

Write your migration manually. E.g. run rails g migration DropUsers.

As for the code of the migration I'm just gonna quote Maxwell Holder's post Rails Migration Checklist

BAD - running rake db:migrate and then rake db:rollback will fail

class DropUsers < ActiveRecord::Migration  def change    drop_table :users  endend

GOOD - reveals intent that migration should not be reversible

class DropUsers < ActiveRecord::Migration  def up    drop_table :users  end  def down    fail ActiveRecord::IrreversibleMigration  endend

BETTER - is actually reversible

class DropUsers < ActiveRecord::Migration  def change    drop_table :users do |t|      t.string :email, null: false      t.timestamps null: false    end  endend