# Django REST framework快速起步

## 安装Django REST framework

* 创建一个Django项目，名为`tutorial`，并且启动一个新的app名字叫`quickstart`

```
# Create the project directory
mkdir tutorial
cd tutorial

# Create a virtualenv to isolate our package dependencies locally
virtualenv env
source env/bin/activate  # On Windows use `env\Scripts\activate`

# Install Django and Django REST framework into the virtualenv
pip install django
pip install djangorestframework

# Set up a new project with a single application
django-admin.py startproject tutorial .  # Note the trailing '.' character
cd tutorial
django-admin.py startapp quickstart
cd ..
```

上述命令已经完成了django目录初始化

* 首次同步数据库

```
python manage.py migrate
```

在CentOS 5.11环境下，由于使用的是sqlite 3.3.6，则会出现以下报错

> 如果使用sqlite 3.8.11则不会出现该问题

```
Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    execute_from_command_line(sys.argv)
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/core/management/__init__.py", line 364, in execute_from_command_line
    utility.execute()
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/core/management/__init__.py", line 356, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/core/management/base.py", line 330, in execute
    output = self.handle(*args, **options)
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 83, in handle
    executor = MigrationExecutor(connection, self.migration_progress_callback)
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/db/migrations/executor.py", line 20, in __init__
    self.loader = MigrationLoader(self.connection)
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/db/migrations/loader.py", line 52, in __init__
    self.build_graph()
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/db/migrations/loader.py", line 209, in build_graph
    self.applied_migrations = recorder.applied_migrations()
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/db/migrations/recorder.py", line 65, in applied_migrations
    self.ensure_schema()
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/db/migrations/recorder.py", line 56, in ensure_schema
    with self.connection.schema_editor() as editor:
  File "/home/admin/tutorial/env/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 25, in __enter__
    self._initial_pragma_fk = c.fetchone()[0]
TypeError: 'NoneType' object has no attribute '__getitem__'
```

这个报错在[migrate and other commands fail with TypeError: 'NoneType' object has no attribute '**getitem**' in schema.py](https://code.djangoproject.com/ticket/26205?cversion=0\&cnum_hist=2)说明：

Django 1.9使用sqlite3 v3.3.6时候会出现`PRAGMA foreign_keys`返回nothing，而不是0或者1。解决方法是修改 `django/db/backends/sqlite3/schema.py`

将

```python
self._initial_pragma_fk = c.fetchone()[0]
```

修改成

```python
self._initial_pragma_fk = 0  # c.fetchone()[0]
```

* 创建一个名为`admin`用户，使用密码`MyPass`

```
python manage.py createsuperuser
```

## 序列化

这里定义一些序列化：创建一个新的模块名为`tutorial/quickstart/serializers.py`用于数据表现：

```python
from django.contrib.auth.models import User, Group
from rest_framework import serializers


class UserSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = User
        fields = ('url', 'username', 'email', 'groups')


class GroupSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Group
        fields = ('url', 'name')
```

注意这里使用超链接`HyperlinkedModelSerializer`。可以使用主键和一些其他关系，不过超链接是一个良好的RESTful设计。

> 注意：这里如果没有使用`from django.db import models`，则会出现报错

```
    model = User
NameError: name `User` is not defined
```

## 视图

现在定义一些视图，编辑`tutorial/quickstart/views.py`添加如下

```python
from django.contrib.auth.models import User, Group
from rest_framework import viewsets
from tutorial.quickstart.serializers import UserSerializer, GroupSerializer


class UserViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows users to be viewed or edited.
    """
    queryset = User.objects.all().order_by('-date_joined')
    serializer_class = UserSerializer


class GroupViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows groups to be viewed or edited.
    """
    queryset = Group.objects.all()
    serializer_class = GroupSerializer
```

和编写多个视图不同，这里将所有共有特性统一存放到`ViewSets`的类中。

## URLs

编写API URLs，则在 `tutorial/urls.py`

```python
from django.conf.urls import url, include
from rest_framework import routers
from tutorial.quickstart import views

router = routers.DefaultRouter()
router.register(r'users', views.UserViewSet)
router.register(r'groups', views.GroupViewSet)

# Wire up our API using automatic URL routing.
# Additionally, we include login URLs for the browsable API.
urlpatterns = [
    url(r'^', include(router.urls)),
    url(r'^api-auth/', include('rest_framework.urls', namespace='rest_framework'))
]
```

由于使用viewsets取代views，可以通过简单在一个router类注册viewsets，这样从API自动生成URLs conf。

如果需要更多API URLs，可以简单通过使用常规基于类的视图，并明确编写URL conf。

最后，包含默认的登陆和登出视图用于浏览API，中国是可选的，但是如果API要求授权并且希望使用可浏览的API，则非常有用。

## 设置

设置一些全局设置，开启页码，并且希望API只被admin用户访问，在设置 `tutorial/settings.py`

```python
INSTALLED_APPS = (
    ...
    'rest_framework',
)

REST_FRAMEWORK = {
    'DEFAULT_PERMISSION_CLASSES': [
        'rest_framework.permissions.IsAdminUser',
    ],
    'PAGE_SIZE': 10
}
```

> 以上完成所有测试代码编写

## 测试API

运行程序

```
python manage.py runserver
```

* 访问APU

```bash
curl -H 'Accept: application/json; indent=4' -u admin:password123 http://127.0.0.1:8000/users/
{
    "count": 2,
    "next": null,
    "previous": null,
    "results": [
        {
            "email": "admin@example.com",
            "groups": [],
            "url": "http://127.0.0.1:8000/users/1/",
            "username": "admin"
        },
        {
            "email": "tom@example.com",
            "groups": [                ],
            "url": "http://127.0.0.1:8000/users/2/",
            "username": "tom"
        }
    ]
}
```

## 参考

* [Django REST framework Quickstart](http://www.django-rest-framework.org/tutorial/quickstart/)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://huataihuang.gitbook.io/cloud-atlas-draft/develop/python/django/rest_framework/django_rest_framework_quickstart.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.