Rails — create and create! methods, RoR 3 Tutorial

问题:

So I know the distinction between the bang (exclamation mark) and non-bang methods usually is whether the method will modify the object itself or return a separate modified object keeping the original unchanged.

Then while building the User model in chapter 6 of the book, I came across the User.create method, which creates a new model and saves it to the database in a single step. In Michael Hartl's Ruby on Rails 3 Tutorial, he writes that the User.create! method "works just like the create method...except that it raises an ActiveRecord::Record-Invalid exception if the creation fails."

I'm pretty confused. Is the User.create! method not following Ruby "bang-convention" or am I completely missing something? And if he IS following the convention, how does User.create! modify self if it is a class method?

回答1:

Though a lot of classes treat bang methods as "a method that modifies the object in place", I like the description of bang methods from the Eloquent Ruby book better:

In practice, Ruby programmers reserve ! to adorn the names of methods that do something unexpected, or perhaps a bit dangerous

So in this case, the "unexpected" result is that an exception is raised instead of just failing and returning false.

回答2:

Hope this helps as well:

The bang versions (e.g. save!) raise an exception if the record is invalid. The non-bang versions don’t: save and update_attributes return false, create and update just return the objects.

Source: http://edgeguides.rubyonrails.org/active_record_validations.html#when-does-validation-happen-questionmark

Edit: Changed source to fix broken link