Generating a migration from model

I am a beginner in Ruby on Rails and following the below article:- http://guides.rubyonrails.org/migrations.html

If I need to generate a migration and a model, I can use, for example :-

$ rails generate model Product name:string description:text

and that would create :-

class CreateProducts < ActiveReco开发者_开发技巧rd::Migration
  def change
    create_table :products do |t|
      t.string :name
      t.text :description

      t.timestamps
    end
  end
end

However, If I have a bigger model (with many properties). I don't want to put all the properties in the "rails generate" command. Can I hand code the model first and then generate the migration from that model file?

Sorry for asking so stupid question. I am just trying to understand.

Generate command is not must to do thing. It's just a script which helps you to automate some job. What exactly this command has done you can see in console after running generate command. It looks like this:

    rails generate scaffold User name:string email:string
      invoke active_record
      create
      db/migrate/20100615004000_create_users.rb
    create
      app/models/user.rb
      invoke
      test_unit
      create
      test/unit/user_test.rb
      create
      test/fixtures/users.yml
      route resources :users
      invoke scaffold_controller
      create
      app/controllers/users_controller.rb
      invoke
      erb
      create
      app/views/users
      create
      app/views/users/index.html.erb
      create
      app/views/users/edit.html.erb
      create
      app/views/users/show.html.erb
      create
      app/views/users/new.html.erb
      create
      app/views/users/_form.html.erb
      invoke
      test_unit
      create
      test/functional/users_controller_test.rb
      invoke
      helper
      create
      app/helpers/users_helper.rb
      invoke
      test_unit
      create
      test/unit/helpers/users_helper_test.rb
      invoke stylesheets
      converted by Web2PDFConvert.com
      create
      public/stylesheets/scaffold.css

You can actually create/modify all files by your hand. But the benefit of using generate is that it automatically invokes all necessary plugins and etc to generate all required files. That's why it's recommended to use generate command even for very complicated models, controllers and etc. So in your case I would suggest to divide the building the model in several steps. It could be like this:

rails generate model Product name:string description:text
rails generate migration AddPriceToProducts price:integer
rails generate migration AddDiscountToProducts discount:integer
and so on

Every step you could rollback in case if you made some mistake and it helps you to not harm your database.

You can hand-code the migration. The model's attributes are read directly from the database... so if you add t.string :name to the migration file, and then run rake db:migrate, that column will be added to the table, therefore making it available as an attribute on your model.