RoR:Mongoid和表单创建哈希 [英] RoR : Mongoid and form create hash

问题描述

Rails专家的简单问题.为什么我必须在我的VideosController的以下创建方法中使用以下语句插入新的Mongoid文档:params [:video] [:description]?为什么我不能使用POST表单中的params [:description]?如果使用它，该值将变为nil.

Simple question for Rails gurus. Why I do have to use the following statement to insert a new Mongoid document : params[:video][:description] in the following create method of my VideosController? Why I can't use the params[:description] from the POST form? If I use it, the value becomes nil.

def create
    @video = Video.new(
        :title => params[:video][:title],
        :description => params[:video][:description]
    )
    if @video.save
        render 'success'
    else
        render 'error'
    end
end

这是Video.rb类:

Here is the Video.rb class :

class Video
    include Mongoid::Document

    field :title, type: String
    field :description, type: String

    validates_presence_of :title
    validates_presence_of :description

    acts_as_url :title
end

最后进入表单视图:

<%=  form_for @video do |f| %>

    <%= f.label :title %>
    <%= f.text_field :title %>

    <p/>

    <%= f.label :description %>
    <%= f.text_field :description %>

    <%= submit_tag("Enqueue video") %>

<% end %>

我不太明白为什么表单输入是video [description]而不只是期望的描述:

I don't quite get why the form input are video[description] and not just description as expected :

<label for="video_title">Title</label>
<input id="video_title" name="video[title]" type="text" />

<p/>

<label for="video_description">Description</label>
<input id="video_description" name="video[description]" type="text" />

推荐答案

使用form_for时:

创建一个允许用户创建或更新属性的表单 特定模型对象的对象.

Creates a form that allows the user to create or update the attributes of a specific model object.

在您的情况下，为Video模型.要了解Rails约定:

In your case, Video model. To understand Rails convention:

<%=  form_for @video do |f| %>
...
<%= f.text_field :description %>
...

这将产生一个html标记，其名称属性为 video [description] .这意味着，提交表单后，用户输入的值将在控制器中显示为 params [:video] [:description] .

Which results in an html tag whose name attribute is video[description]. This means that when the form is submitted, the value entered by the user will be available in the controller as params[:video][:description].

根据文档，params变量是ActiveSupport::HashWithIndifferentAccess的实例，就像Hash一样，差别很小:

The params variable is an instace of ActiveSupport::HashWithIndifferentAccess, like a Hash with a small difference, according to documentation:

此类具有可疑的语义，我们只有这样才能使人们 可以编写 params [:key] 而不是 params ['key'] ，它们得到的结果相同 两个键的值.

This class has dubious semantics and we only have it so that people can write params[:key] instead of params[‘key’] and they get the same value for both keys.

您的params类似于:

{"utf8"=>"✓",
 "_method"=>"post",
 "authenticity_token"=>"xxx",
 "video"=>
  {"description"=>"Video desc"}
}

其中"video"或:video是哈希的键之一.因此，params[:video]等效于params.fetch("video")，其值为{"description"=>"Video desc"}.如您所见，该值是另一个哈希.最后，要获取描述的值，您必须先params[:video][:description](Rails方式)或params.fetch("video").fetch("description")，其值是"Video desc".

Where "video" or :video is one of the keys of the Hash. So, params[:video] is equivalent to params.fetch("video") which value is {"description"=>"Video desc"}. As you can see the value is another Hash. Finally to get the value of the description you have to params[:video][:description] (The Rails way) or params.fetch("video").fetch("description"), which value is "Video desc".

fetch是Hash的Ruby方法:从哈希中返回给定键的值."

fetch is a Ruby method of Hash: "Returns a value from the hash for the given key."

考虑到这一点:

Video.new(params[:video]) = Video.new(:description => "Video desc") = Video.new(:description => params[:video][:description])

使用约定更容易，但是请确保您可以使用params[:description](以防万一):

It's easier to use conventions, but for sure you can have params[:description] (just in case):

<%=  form_for @video do |f| %>
...
<%= text_field_tag :description %>
...

请注意，我使用的是text_field_tag而不是f.text_field.在这种情况下，params哈希中的html标签名称将为description，您将收到{ "description" => 'Video desc" } ...

Note that I'm using text_field_tag instead of f.text_field. In this case the html tag name will be description in the params Hash you will receive { "description" => 'Video desc" }...

请访问 Rails API文档，以了解不同的帮助程序等.此外，还请查看服务器的日志.

Take a look to Rails API documentation to understand different helpers, etc. And also review your server's log.

这篇关于RoR:Mongoid和表单创建哈希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！