Quick Start

Yii provides a whole set of tools to simplify the task of implementing RESTful Web Service APIs. In particular, Yii supports the following features about RESTful APIs:

• Quick prototyping with support for common APIs for Active Record;
• Response format negotiation (supporting JSON and XML by default);
• Customizable object serialization with support for selectable output fields;
• Proper formatting of collection data and validation errors;
• Collection pagination, filtering and sorting;
• Support for HATEOAS;
• Efficient routing with proper HTTP verb check;
• Built-in support for the OPTIONS and HEAD verbs;
• Authentication and authorization;
• Data caching and HTTP caching;
• Rate limiting;

In the following, we use an example to illustrate how you can build a set of RESTful APIs with some minimal coding effort.

Assume you want to expose the user data via RESTful APIs. The user data are stored in the user DB table, and you have already created the active record class app\models\User to access the user data.

Creating a Controller

First, create a controller class app\controllers\UserController as follows:

namespace app\controllers;

use yii\rest\ActiveController;

class UserController extends ActiveController
{
    public $modelClass = 'app\models\User';
}

The controller class extends from yii\rest\ActiveController, which implements a common set of RESTful actions. By specifying modelClass as app\models\User, the controller knows which model can be used for fetching and manipulating data.

Configuring URL Rules

Then, modify the configuration of the urlManager component in your application configuration:

'urlManager' => [
    'enablePrettyUrl' => true,
    'enableStrictParsing' => true,
    'showScriptName' => false,
    'rules' => [
        ['class' => 'yii\rest\UrlRule', 'controller' => 'user'],
    ],
]

The above configuration mainly adds a URL rule for the user controller so that the user data can be accessed and manipulated with pretty URLs and meaningful HTTP verbs.

Note: Yii will automatically pluralize controller names for use in endpoints (see Trying it Out section below). You can configure this using the yii\rest\UrlRule::$pluralize property.

Enabling JSON Input

To let the API accept input data in JSON format, configure the parsers property of the request application component to use the yii\web\JsonParser for JSON input:

'request' => [
    'parsers' => [
        'application/json' => 'yii\web\JsonParser',
    ]
]

Info: The above configuration is optional. Without the above configuration, the API would only recognize application/x-www-form-urlencoded and multipart/form-data input formats.

Trying it Out

With the above minimal amount of effort, you have already finished your task of creating the RESTful APIs for accessing the user data. The APIs you have created include:

• GET /users: list all users page by page;
• HEAD /users: show the overview information of user listing;
• POST /users: create a new user;
• GET /users/123: return the details of the user 123;
• HEAD /users/123: show the overview information of user 123;
• PATCH /users/123 and PUT /users/123: update the user 123;
• DELETE /users/123: delete the user 123;
• OPTIONS /users: show the supported verbs regarding endpoint /users;
• OPTIONS /users/123: show the supported verbs regarding endpoint /users/123.

You may access your APIs with the curl command like the following,

$ curl -i -H "Accept:application/json" "http://localhost/users"

HTTP/1.1 200 OK
...
X-Pagination-Total-Count: 1000
X-Pagination-Page-Count: 50
X-Pagination-Current-Page: 1
X-Pagination-Per-Page: 20
Link: <http://localhost/users?page=1>; rel=self, 
      <http://localhost/users?page=2>; rel=next, 
      <http://localhost/users?page=50>; rel=last
Transfer-Encoding: chunked
Content-Type: application/json; charset=UTF-8

[
    {
        "id": 1,
        ...
    },
    {
        "id": 2,
        ...
    },
    ...
]

Try changing the acceptable content type to be application/xml, and you will see the result is returned in XML format:

$ curl -i -H "Accept:application/xml" "http://localhost/users"

HTTP/1.1 200 OK
...
X-Pagination-Total-Count: 1000
X-Pagination-Page-Count: 50
X-Pagination-Current-Page: 1
X-Pagination-Per-Page: 20
Link: <http://localhost/users?page=1>; rel=self, 
      <http://localhost/users?page=2>; rel=next, 
      <http://localhost/users?page=50>; rel=last
Transfer-Encoding: chunked
Content-Type: application/xml

<?xml version="1.0" encoding="UTF-8"?>
<response>
    <item>
        <id>1</id>
        ...
    </item>
    <item>
        <id>2</id>
        ...
    </item>
    ...
</response>

The following command will create a new user by sending a POST request with the user data in JSON format:

$ curl -i -H "Accept:application/json" -H "Content-Type:application/json" -XPOST "http://localhost/users" -d '{"username": "example", "email": "user@example.com"}'

HTTP/1.1 201 Created
...
Location: http://localhost/users/1
Content-Length: 99
Content-Type: application/json; charset=UTF-8

{"id":1,"username":"example","email":"user@example.com","created_at":1414674789,"updated_at":1414674789}

Tip: You may also access your APIs via Web browser by entering the URL http://localhost/users. However, you may need some browser plugins to send specific request headers.

As you can see, in the response headers, there is information about the total count, page count, etc. There are also links that allow you to navigate to other pages of data. For example, http://localhost/users?page=2 would give you the next page of the user data.

Using the fields and expand parameters, you may also specify which fields should be included in the result. For example, the URL http://localhost/users?fields=id,email will only return the id and email fields.

Info: You may have noticed that the result of http://localhost/users includes some sensitive fields, such as password_hash, auth_key. You certainly do not want these to appear in your API result. You can and should remove these fields from result as described in the Resources section.

Addionally, you can sort collections like http://localhost/users?sort=email or http://localhost/users?sort=-email. Filtering collections like http://localhost/users?filter[id]=10 or http://localhost/users?filter[email][like]=gmail.com could be implemented using data filters. See Resources section for details.

Summary

Using the Yii RESTful API framework, you implement an API endpoint in terms of a controller action, and you use a controller to organize the actions that implement the endpoints for a single type of resource.

Resources are represented as data models which extend from the yii\base\Model class. If you are working with databases (relational or NoSQL), it is recommended you use ActiveRecord to represent resources.

You may use yii\rest\UrlRule to simplify the routing to your API endpoints.

While not required, it is recommended that you develop your RESTful APIs as a separate application, different from your Web front end and back end for easier maintenance.