小编jee*_*ace的帖子

add_index :microposts, [:user_id, :created_at]

我正在阅读Michael Hartl的轨道教程,并注意到他正在使用一种称为多键索引的东西.我知道这意味着Active Record同时使用两个键,但我不确定使用多个键索引的优点和缺点是什么.

如果有人能给出答案我会非常感激.

我刚刚上传了这个问题,但它最终给了我的风滚草徽章,所以我再试一次.

我现在正在阅读迈克尔·哈特尔的铁路教程,我遇到了一个问题,即盒子大小的属性干扰了表格高度,如下图所示.

@mixin box_sizing {
  -moz-box-sizing: border-box;
  -webkit-box-sizing: border-box;
  box-sizing: border-box;
}

input, textarea, select, .uneditable-input {
  border: 1px solid #bbb;
  width: 100%;
  height: auto;
  margin-bottom: 15px;
  @include box_sizing; <--- this line here is causing issues
}

(有效的盒子大小属性)

(box-sizing属性无效)

注意当box-sizing属性生效时,有多少小形式？您无法真正查看完整的字母,因为高度太低.我试图在输入,textarea,..等下更改height属性.但好像我的代码被Bootstrap覆盖了.如果你有任何想法如何使形式更大(更高的高度)我会非常感激.

我正在尝试关注jQuery-FileUpload上的Railscasts剧集.我已经添加

gem 'jquery-fileupload-rails' 

到了资产组Gemfile,还加了

//= require jquery-fileupload/basic

line到application.js资源目录中的文件.但是,当我尝试调出网站时,会显示以下错误:

couldn't find file 'jquery-fileupload'
  (in root/app/assets/javascripts/application.js:15)

任何帮助将不胜感激.

我有一个mongodb/mongoskin聚合请求如下:

db.collection(customerTable + '_earnedinfluencers').aggregate([
    {
        $group: {
            _id: '$user',
            name: '', // to be filled separately
            username: '', // to be filled separately 
            picture: '', // to be filled separately
            city: '', // to be filled separately
            kids: { $sum: '$kids' },
            revenue: { $sum: '$dayIncome' },
            kidsRevRatio: { $divide: [ { $sum: '$kids' }, { $sum: '$dayIncome' } ] }
        }, 

        $match: {
            richness: { $gte: variable1 },
            kids: { $lt: variable2 },
            hobbies: { $in: ['hobby1', 'hobby2', 'hobby3', …

我正在阅读懒惰的评估,并且无法理解他们给出的基本示例.

#lang racket
(define (bad-if x y z)
  (if x y z))
(define (factorial-wrong x)
  (bad-if (= x 0)
          1
          (* x (factorial-wrong (- x 1)))))

(factorial-wrong 4)

我有点困惑为什么这个程序永远不会终止.我知道下面的代码工作得很好:

(define (factorial x)
  (if (= x 0)
      1
      (* x (factorial (- x 1)))))

(factorial 4)

所以我假设它与范围有关.我尝试了一步一步的调试,即使x被映射到0,factorial-wrong也会执行递归函数.

我正在经历一个codeacademy的javascript练习并遇到了这个问题.codeacademy给出了以下代码.

var friends = {
    bill: {
        firstName: "Bill",
        lastName: "Gates",
        number: "1",
        address: ['abc', 'def', 'ghi']
    },
    steve: {
        firstName: "Steve",
        lastNAme: "Jobs",
        number: "2",
        address: ['abc', 'def', 'ghi']
    }
};

var list = function(obj) {
    for (var prop in obj) {
        console.log(prop);
    }
};

var search = function(name) {
    for (var prop in friends) {
        if (friends[prop].firstName === name) {
            console.log(friends[prop]);
            return friends[prop];
        }
    }
};

我不明白的是,在搜索功能中,为什么我需要写出'friends [prop]'而不仅仅是'prop'.如果for/in循环遍历friends中的每个属性(数组？),为什么我需要再次指定每个prop所属的数组？为什么我不能使用以下代码？

var search = function(name) {
    for (var prop in friends) …

我正在尝试创建一个显示模型所有注释的Feed.

_comments.html.erb

<% if @comments.any? %>
    <ol>
      <%= render partial: 'shared/comment_feed', collection: @comments %>
    </ol>
    <%= will_paginate @comments %>
<% else %>
    <h2>Be the first one to comment on this episode!</h2>
<% end %>

_comment_feed.html.erb

<li id="<%= comment.id %>">
  <%= link_to gravatar_for(comment.user), comment.user %>
  <span class="user">
    <%= link_to comment.user.name, comment.user %>
  </span>
  <span class="content"><%= simple_format comment.content %></span>
  <span class="timestamp">
    Posted <%= time_ago_in_words(comment.created_at) %> ago.
  </span>
  <% if current_user?(comment.user) %>
    <%= link_to "delete", comment, method: :delete,
                                   confirm: "Are you sure?",
                                   title: …