def to_s 函数是什么? [英] What is the def to_s function?

问题描述

我正在浏览Blogger<的标签"部分/a> 教程，我对一个部分有点困惑:def to_s 函数(在 tag.rb 中)；为什么需要它以及它是如何包含的.

I'm going through the "Tags" section of the Blogger tutorial and am a bit confused on one part: the def to_s function (in tag.rb); why it's required and how it's included.

为了上下文，我已经包含了相关文件的一些相关部分.

I've included some relevant parts of relevant files for context.

模型

article.rb

class Article < ActiveRecord::Base
  attr_accessible :tag_list
  has_many :taggings
  has_many :tags, through: :taggings

  def tag_list
    return self.tags.collect do |tag|
      tag.name
    end.join(", ")
  end

  def tag_list=(tags_string)
    self.taggings.destroy_all

      tag_names = tags_string.split(",").collect{|s| s.strip.downcase}.uniq

      tag_names.each do |tag_name|
        tag = Tag.find_or_create_by_name(tag_name)
        tagging = self.taggings.new
        tagging.tag_id = tag.id
      end
    end
  end

tag.rb

class Tag < ActiveRecord::Base
  has_many :taggings
  has_many :articles, through: :taggings

  def to_s
    name
  end
end

标签.rb

class Tagging < ActiveRecord::Base
  belongs_to :tag
  belongs_to :article
end

控制器

tags_controller.rb

class TagsController < ApplicationController

  def index
    @tags = Tag.all
  end

  def show
    @tag = Tag.find(params[:id])
  end

  def destroy
    @tag = Tag.find(params[:id]).destroy
    redirect_to :back
  end
end

帮助

articles_helper.rb

module ArticlesHelper

  def tag_links(tags)
    links = tags.collect{|tag| link_to tag.name, tag_path(tag)}
    return links.join(", ").html_safe
  end
end

视图

new.html.erb

<%= form_for(@article, html: {multipart: true}) do |f| %>
  <p>
    <%= f.label :tag_list %>
    <%= f.text_field :tag_list %>
  </p>
  <p>
    <%= f.submit %>
  </p>
<% end %>

show.html.erb

标签:<%= tag_links(@article.tags) %>

推荐答案

我明白你的意思.当您在字符串中连接值时，您必须编写例如

I got your point. When you concatenate value in string you have to write eg

"hello #{@user.name}" 

因此，不是调用@user.name，您可以指定您必须将用户显示为字符串的任何内容，您可以直接在 to_s 方法中指定，这样您就不需要再次调用 .to_s 只需编写

So instead of calling @user.name u can specify whatever u have to display user as a string you can directly specify in to_s method so that you dont need to call .to_s again just write

"hello #{@user}"

在上面的代码行中搜索@user 类的 .to_s 方法并打印返回值.

above line of code search for .to_s method for @user's class and print returning value.

同样适用于像

user_path(@user)

会给你 >> users/123 # 其中 123 是@user 的 id

will give you >> users/123 # where 123 is id of @user

如果你写

def to_params
 self.name
end

然后它会给出 >> users/john # 其中 john 是@user 的名字

Then it will give >> users/john # where john is the @user's name

这篇关于def to_s 函数是什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！