A Rails Model is a Ruby class that can add database records (think of whole rows in an Excel table), find particular data you're looking for, update that data, or remove data. These common operations are referred to by the acronym CRUD--Create, Remove, Update, Destroy.
To generate a fully working scaffold for a new object, including model, controller, views, assets, and tests, use the rails g scaffold command. Then you can run rake db:migrate to set up the database table. Then you can visit http://localhost:3000/widgets and you'll see a fully functional CRUD scaffold.
Active Model allows for Action Pack helpers to interact with plain Ruby objects. Active Model also helps build custom ORMs for use outside of the Rails framework. After reading this guide, you will know: How an Active Record model behaves.
The code is okay but you are in the wrong directory. You must run these commands inside your rails project-directory.
The normal way to get there from scratch is:
$ rails new PROJECT_NAME
$ cd PROJECT_NAME
$ rails generate model ad \
name:string \
description:text \
price:decimal \
seller_id:integer \
email:string img_url:string
The error shows you either didn't create the rails project yet or you're not in the rails project directory.
Suppose if you're working on myapp project. You've to move to that project directory on your command line and then generate the model. Here are some steps you can refer.
Example: Assuming you didn't create the Rails app yet:
$> rails new myapp
$> cd myapp
Now generate the model from your commandline.
$> rails generate model your_model_name
You need to create new rails application first. Run
rails new mebay
cd mebay
bundle install
rails generate model ...
And try to find Rails 3 tutorial, there are a lot of changes since 2.1 Guides (http://guides.rubyonrails.org/getting_started.html) are good start point.
For me what happened was that I generated the app with rails new rails new chapter_2 but the RVM --default had rails 4.0.2 gem, but my chapter_2 project use a new gemset with rails 3.2.16.
So when I ran
rails generate scaffold User name:string email:string
the console showed
Usage:
rails new APP_PATH [options]
So I fixed the RVM and the gemset with the rails 3.2.16 gem , and then generated the app again then I executed
rails generate scaffold User name:string email:string
and it worked
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