Rails : How does “new” action called “create” acti

问题:

I am following this tutorial http://guides.rubyonrails.org/v3.2.13/getting_started.html to build my rails app in version 3.2.13 . If you go to the section 6.9 you will find controller and view for creating new posts . Here I do not get how @post variable is passed from new action to create action and where is create function called ? Also , I faced the same problem while working on edit and update actions . Please guide me through this .

回答1:

It's not passed to create action, it's instantiated again with params you pass from the form displayed with new action.

create action is called with POST request to the path specified in config/routes.rb, leading to specific controller and action.

回答2:

@post is not passed from new to create the params hash is passed into the create method @post is then set using the new method of the model not the controller. create calls new and then save and returns the object. new returns the object without saving and then save returns the validity of the object. That is why the create method in the controller calls new and then has a conditional statement for save. It is basically saying initialize this object then if it is a valid object do one thing if it is not do another. The create action is not called because of this check.

#this will return true if valid or false if invalid
  Post.new(params[:post]).save 
#this will always return the Post object which conditionally is true in Ruby
  Post.create(params[:post])
#To use the create in a conditional statement it would be 
  Post.create(params[:post]).valid? || Post.create(param[:post]).save

The last line is unnecessarily redundant and thus why the example uses new followed by save.

create method for a Model is more succinct but probably best to use when you know the object is valid.

Hope this gives you a better understanding but if you are still confused please let me know and I will try to explain further.