Question

I am trying to accomplish the atypical library learning a language application. I have been able to create Books, People, and BookCheckOuts. I’ve got the relationships working pretty well but am having issues with wrapping my head around how to handle books that have never been checked out.

I’ve created two properties on my book class CheckedOut (returns a boolean) and LastCheckedOutTo (returns a person). I am pretty much at peace with CheckedOut and feel confident that I am using the right RoR mechanism for determining if a book is presently checked out and returning a boolean in either case. I am not as confident about LastCheckedOutTo as my implementation seems like a kludge.

Am I going about this correctly? Is there a better way?

Book Class in its Entirety

class Book < ActiveRecord::Base
  has_many :book_check_outs
  has_many :people, :through => :book_check_outs

  def checked_out
    if (book_check_outs.find(:first, :conditions => "return_date is null"))
      true
    else
      false
    end
  end

  def last_checked_out_to
    if (book_check_outs.count > 0)
      book_check_outs.find(:first,
        :order => "out_date desc").person
    else
      Person.new()
    end
  end
end

Answer 1

Perhaps:

class Book < ActiveRecord::Base
  has_many :book_loans
  has_many :borrowers, :class_name => 'Person', :through => :book_loans

  def loaned?
    book_loans.exists?(:return_date => nil)
  end

  # I would be reluctant to return a new Person object
  #  just because it was not checked out by anyone, instead you could return nil
  #  OR exception out.   
  def current_borrower
    book_loans.first(:order => "out_date desc").person 
  end
end

# you can use a helper to keep your presentation clean 
module BookHelper 
  def borrower_name(book)
     if borrower = book.borrower
       borrower.name 
     else 
       "not checked out" 
     end
  end
end