Rails: How to run `rails generate scaffold` when the model already exists?

TL;DR: rails g scaffold_controller <name>

Even though you already have a model, you can still generate the necessary controller and migration files by using the rails generate option. If you run rails generate -h you can see all of the options available to you.

Rails:  controller  generator  helper  integration_test  mailer  migration  model  observer  performance_test  plugin  resource  scaffold  scaffold_controller  session_migration  stylesheets

If you'd like to generate a controller scaffold for your model, see scaffold_controller. Just for clarity, here's the description on that:

Stubs out a scaffolded controller and its views. Pass the model name, either CamelCased or under_scored, and a list of views as arguments. The controller name is retrieved as a pluralized version of the model name.

To create a controller within a module, specify the model name as a path like 'parent_module/controller_name'.

This generates a controller class in app/controllers and invokes helper, template engine and test framework generators.

To create your resource, you'd use the resource generator, and to create a migration, you can also see the migration generator (see, there's a pattern to all of this madness). These provide options to create the missing files to build a resource. Alternatively you can just run rails generate scaffold with the --skip option to skip any files which exist :)

I recommend spending some time looking at the options inside of the generators. They're something I don't feel are documented extremely well in books and such, but they're very handy.

Great answer by Lee Jarvis, this is just the command e.g; we already have an existing model called User:

rails g scaffold_controller User

For the ones starting a rails app with existing database there is a cool gem called schema_to_scaffold to generate a scaffold script.it outputs:

rails g scaffold users fname:string lname:string bdate:date email:string encrypted_password:string

from your schema.rb our your renamed schema.rb. Check it