Return JSON with CodeIgniter

With the ever-increasing use of Javascript and AJAX related calls, it’s would be nice to be able to quickly build endpoints that returned JSON data for our web site. Whether your rolling your own code, using jQuery or using third-party tools like KendoUI, it’s very easy to return structured data in JSON format using CodeIgniter, a PHP framework from the fine folks at EllisLab.

随着与Javascript和AJAX相关的请求不断增长，最好能够快速构建能够为我们的网站返回JSON数据的端点。不论你是自己写代码、或者用jQuery、或者像 KendoUI一样的第三方工具，CodeIgniter都能很方便地返回JSON格式的结构化数据。CodeIgniter是一个由EllisLab的家伙们构造的PHP框架。

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CodeIgniter uses a simplified Model-View-Controller pattern to help you build websites quickly without worrying about the plumbing code that seems to go into every web site you build. In a typical CI web site, each page request, calls a controller which is responsible for determining what data gets loaded and which view of the data will be presented to the requester. When loaded, the model is responsible for determining how the data is retrieved. This data is then returned to the controller which passes it on to a View. Views are responsible for taking the structured data and formatting it for presentation to the user (typically in HTML).

CI使用了一个简化的MVC模式来帮助你快速构建站点，从而使你不在受累于每个站点中都有的那些样板代码。在一个典型的CI站点中，每一个页面请求都调用一个控制器，由它来决定哪些数据被装载以及这些数据对应的哪个视图被呈现给用户。当模型被装载之后，它负责数据的获取。然后数据被返回给控制器，控制器把它们传递给视图。视图负责接收这些结构化的数据，并且将它们格式化以后呈现给用户（通常在HTML中）。

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In this article, we’re going to look a quick and easy way to present that same data as JSON when we need it.

在这篇文章中，我们将要快速而简要地看一下当需要时怎么把这些数据用JSON格式呈现。

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First, let’s take a look at our controller. We’ll use the index function which is called by default when no other function is defined in the page request URI. We’ll be passing our product ID into this function as part of the URI and CodeIgniter will use it as the $product_id parameter for this function.

首先来看一下我们的控制器。我们将使用index函数，当页面请求URI中没有其它函数时，index函数就会被调用。我们将把product ID作为URI的一部分传递给这个函数，CI将把它用作这个函数的参数$product_id。

／／product.php
<?php      
  class Product extends CI_Controller      
  {          
    function index($product_id)          
    {                 
       $this->load->model('Product_model', 'product');
       $data['json'] = $this->product->get($product_id);
       if (!$data['json']) show_404();
 
       $this->load->view('json_view', $data);
    }
  }
?>

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The controller will load our product model and then call the get method, passing in the $product_id parameter. The result of this method is stored into an element in an array called $data using the key ‘json’. We then check to make sure that we actually returned a product. If not, we’ll present a ’404 – Not Found’ error to the user’s browser. This is cleaner and safer than just sending back empty data.

这个控制器将会加载我们的product模型，并且调用get方法，传递进去$product_id 作为参数。这个方法的返回值被存储于 $data数组的一个元素中，以'josn'作为键。然后我们参查是不是的确返回了一个product。如果不是的话，就在用户的浏览器中呈现一个'404-Not Found'错误。这比我们直接发送一个空数据要更整洁和安全。

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／／product_model.php
<?php   
  class Product_model extends CI_Model  
  {     
    function get($product_id)     
    {