ruby-on-rails - 当使用 "find_all_by"时，为什么使用 :order => :title rather than :order => title

Question

在查看 haml 文件中我有一个链接，当您单击时，您会看到所有按标题或发布日期排序的电影。 Controller 中的代码是:

def index
    sort = params[:sort] || session[:sort]
    case sort
    when 'title'
      ordering,@title_header = {:order => :title}, 'hilite'
    when 'release_date'
      ordering,@date_header = {:order => :release_date}, 'hilite'
    end
   # some more codes here
@movies = Movie.find_all_by_rating(@selected_ratings.keys, ordering)
end

如果我改变

ordering,@title_header = {:order => :title}, 'hilite'
到

 ordering,@title_header = {:order => title}, 'hilite'

报错:

undefined local variable or method `title' for #<MoviesController:0xb29a853c>

Answer 1

{:order => :title}

{:order => 'title'}

两者都有效。查看此线程以了解字符串和符号之间的差异:What's the difference between a string and a symbol in Ruby?

{:order => title}

不起作用，因为您试图为您的散列键分配一个包含在 title 局部变量中的值，但它不存在，因此它崩溃了