Running `rails generate scaffold` on an existing model in Rails

If you have an existing model in your Rails application and want to generate a scaffold for it, you can use the rails generate scaffold command with the appropriate options.

Step 1: Generate the Scaffold

The first step is to run the command with the name of your existing model:

rails generate scaffold ModelName

Replace ModelName with the name of your existing model.

This will generate the necessary files for a scaffold, including a controller, views, and routes.

Step 2: Modify the Controller

Since you already have a model, you will need to modify the generated controller to use the existing model. Open the generated controller file, which will be located at app/controllers/model_names_controller.rb.

Replace ModelName with the name of your existing model in the following lines:

class ModelNamesController < ApplicationController
  before_action :set_model_name, only: [:show, :edit, :update, :destroy]

  # ...

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_model_name
      @model_name = ModelName.find(params[:id])
    end

    # ...

    # Only allow a list of trusted parameters through.
    def model_name_params
      params.require(:model_name).permit(:attribute1, :attribute2)
    end
end

Step 3: Modify the Views

You will also need to modify the generated views to use your existing model. Open the generated views, which will be located in the app/views/model_names directory.

Replace ModelName with the name of your existing model in the following files:

• _form.html.erb
• edit.html.erb
• index.html.erb
• new.html.erb
• show.html.erb

In each of these files, replace model_name with the name of your existing model in the form fields and any other references to the model.

Conclusion

By following these steps, you can generate a scaffold for an existing model in your Rails application and modify the generated files to use your existing model. This can save you time and effort in setting up a new scaffold from scratch.