About the present method in rails, how to use?

rubyonrails-talk
1

Hi, guys

I read this book ‘Agile web development with rails’ and know this method present, so i have some question. How to use this present method? What is the usage of this method ? Can you give me a example for explaining it?

Thanks a lot.

2

Hey

First, be careful, the name of the method is actually "present?", with the '?'. There is another method called "blank?", what this last method does is asking if an object (or variable) is, let's say, in a 'black state', that is whether it is nil, empty or an empty string and returns true. So you would do things like:

book = ""

if book.blank?   book = writer.write_book else   speaker.read_book(book) end

We are asking if the book has something written on it, and if it doesn't, we write something on it, otherwise, just read it. As you can see, book is "" which is an empty string, so something will be written there.

If you go and check the source code (present? (Object) - APIdock) of "present?", you will find this :

def present?   !blank? end

From this we can say that an object will return true if it is NOT blank. To summarize, "present?" checks if an object is nil, or empty, or "" and returns false if the object is in fact in one of the previous states, otherwise it returns true.

So we could rewrite the previous example as

if book.present?   speaker.read_book(book) else   book = writer.write_book end

Hope this helps!

3

Many thanks to Alejandro, that is very helpful.