Ruby - 嵌套的IF语句语法

Question

I'm trying to get this nested if statement to work but my syntax is wrong and I can't figure it out. I have a search box on a Rails 4 app and a sort dropdown. On the search results page, I want to sort product listings based on what the user selects in the sort dropdown. If a user doesn't enter a search term, I want a message to display. Here is my controller code.

If I remove conditions and just display a default sort, search results page displays fine so the error is in the if statement syntax.

def search
    if params[:search].present?

      if params[:sort] == "- Price - Low to High"
        @listings = ...
      elsif params[:sort] == "- Price - High to Low"
        @listings = ...
      elsif params[:sort] == "- New Arrivals"
        @listings = ...
      elsif params[:sort] == "- Random Shuffle"
        @listings = ...
      else
        @listings = ...
      end

    else
      flash[:notice] = "Please enter one or more search terms e.g. blue shirt."
    end

  end

Answer 1

What you want here is a case statement, a switch from other languages like JavaScript and C:

def search
  if params[:search].present?
    @listings =
      case (params[:sort])
      when  "- Price - Low to High"
        ...
      when "- Price - High to Low"
        ...
      when "- New Arrivals"
        ...
      when "- Random Shuffle"
        ...
      else
        ...
      end
  else
    flash[:notice] = "Please enter one or more search terms e.g. blue shirt."
  end
end

In Ruby, the result of a case statement can be used to assign to a variable, so that eliminates a lot of the @listings = repetition. Same goes for an if .

The things you're comparing against here seem unusually specific. If you've got a drop-down listing that's being used to choose sort order, they should have more succinct values used internally, such as plh to represent "Price - Low to High", or even numerical codes. That means if the phrasing is changed your code still works.

Answer 2

I would change your drop down to have values like price asc , price desc , arrival_date asc (not sure about random shuffle) then you could use.

def search
  if params[:search].present?
    sort_listings(params[:sort])
  else
    flash[:notice] = "Please enter one or more search terms e.g. blue shirt."
  end
end

def sort_listings(sort)
  @listings ||= ...
  @listing.order(sort)
end