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. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
Alejandro Cadavid
2011-Aug-07 14:08 UTC
Re: About the present method in rails, how to use?
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 (http://apidock.com/rails/Object/present%3F) 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! On Sun, Aug 7, 2011 at 7:45 AM, coolesting <coolesting-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:> 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. > > -- > You received this message because you are subscribed to the Google Groups > "Ruby on Rails: Talk" group. > To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > To unsubscribe from this group, send email to > rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > For more options, visit this group at > http://groups.google.com/group/rubyonrails-talk?hl=en. >-- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
Many thanks to Alejandro, that is very helpful. 2011/8/7 Alejandro Cadavid <acadavid-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>> 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 > (http://apidock.com/rails/Object/present%3F) 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! > > On Sun, Aug 7, 2011 at 7:45 AM, coolesting <coolesting-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote: > > 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. > > > > -- > > You received this message because you are subscribed to the Google Groups > > "Ruby on Rails: Talk" group. > > To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > > To unsubscribe from this group, send email to > > rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > > For more options, visit this group at > > http://groups.google.com/group/rubyonrails-talk?hl=en. > > > > -- > You received this message because you are subscribed to the Google Groups > "Ruby on Rails: Talk" group. > To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > To unsubscribe from this group, send email to > rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > For more options, visit this group at > http://groups.google.com/group/rubyonrails-talk?hl=en. > >-- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.