Creating new project:

rails new blog
bundle install

One-to-many relationships:

rails g model Post title:string body:text
rails g model Comment name:string body:text post:references

Then in post.rb add:

has_many :comments, dependent: :destroy

dependent: :destroy, removes all comments related to a post when you delete it.

Notice that in comment.rb, you have this line:

...
    belongs_to :post
...

 

Some paths for the templates (views):

root_path
new_post_path
edit_post_path
post_path

render, just includes the file (html.erb), while redirect_to opens the page:

render 'new'
redirect_to @post

To cancel the last migration:

rake db:rollback STEP=1