如何使用会话P

Django 是支持匿名会话的。会话框架允许您基于每个站点访问者存储和检索任意数据。它在服务器端存储数据并提供cookie的发送和接收。Cookie包含会话ID - 而不是数据本身（除非您使用基于cookie的后端）。

打开会话P

会话通过配置一个中间件实现的

为了打开会话，需要做下面的操作

编辑设置中的 MIDDLEWARE，并确保他包含了 'django.contrib.sessions.middleware.SessionMiddleware'。通过 django-admin startproject 创建的默认 settings.py 文件是已经打开了 SessionMiddleware 这项设置的。

如果你不想使用会话功能，你可以从配置的 MIDDLEWARE 中删除 `SessionMiddleware，并且从 INSTALLED_APPS 中删除 'django.contrib.sessions'。它将会为您节省一点开销。

Configuring the session engineP

By default, Django stores sessions in your database (using the model django.contrib.sessions.models.Session). Though this is convenient, in some setups it's faster to store session data elsewhere, so Django can be configured to store session data on your filesystem or in your cache.

Using database-backed sessionsP

If you want to use a database-backed session, you need to add 'django.contrib.sessions' to your INSTALLED_APPS setting.

Once you have configured your installation, run manage.py migrate to install the single database table that stores session data.

Using cached sessionsP

For better performance, you may want to use a cache-based session backend.

To store session data using Django's cache system, you'll first need to make sure you've configured your cache; see the cache documentation for details.

警告

You should only use cache-based sessions if you're using the Memcached cache backend. The local-memory cache backend doesn't retain data long enough to be a good choice, and it'll be faster to use file or database sessions directly instead of sending everything through the file or database cache backends. Additionally, the local-memory cache backend is NOT multi-process safe, therefore probably not a good choice for production environments.

If you have multiple caches defined in CACHES, Django will use the default cache. To use another cache, set SESSION_CACHE_ALIAS to the name of that cache.

Once your cache is configured, you've got two choices for how to store data in the cache:

Set SESSION_ENGINE to "django.contrib.sessions.backends.cache" for a simple caching session store. Session data will be stored directly in your cache. However, session data may not be persistent: cached data can be evicted if the cache fills up or if the cache server is restarted.
For persistent, cached data, set SESSION_ENGINE to "django.contrib.sessions.backends.cached_db". This uses a write-through cache -- every write to the cache will also be written to the database. Session reads only use the database if the data is not already in the cache.

Both session stores are quite fast, but the simple cache is faster because it disregards persistence. In most cases, the cached_db backend will be fast enough, but if you need that last bit of performance, and are willing to let session data be expunged from time to time, the cache backend is for you.

If you use the cached_db session backend, you also need to follow the configuration instructions for the using database-backed sessions.

Using file-based sessionsP

To use file-based sessions, set the SESSION_ENGINE setting to "django.contrib.sessions.backends.file".

You might also want to set the SESSION_FILE_PATH setting (which defaults to output from tempfile.gettempdir(), most likely /tmp) to control where Django stores session files. Be sure to check that your Web server has permissions to read and write to this location.

Using sessions in viewsP

When SessionMiddleware is activated, each HttpRequest object -- the first argument to any Django view function -- will have a session attribute, which is a dictionary-like object.

You can read it and write to request.session at any point in your view. You can edit it multiple times.

class backends.base.SessionBaseP

This is the base class for all session objects. It has the following standard dictionary methods:

__getitem__(key)P: Example: fav_color = request.session['fav_color']

__setitem__(key, value)P: Example: request.session['fav_color'] = 'blue'

__delitem__(key)P: Example: del request.session['fav_color']. This raises KeyError if the given key isn't already in the session.

__contains__(key)P: Example: 'fav_color' in request.session

get(key, default=None)P: Example: fav_color = request.session.get('fav_color', 'red')

pop(key, default=__not_given)P: Example: fav_color = request.session.pop('fav_color', 'blue')

keys()P

items()P

setdefault()P

clear()P

It also has these methods:

flush()P: Deletes the current session data from the session and deletes the session cookie. This is used if you want to ensure that the previous session data can't be accessed again from the user's browser (for example, the django.contrib.auth.logout() function calls it).

set_test_cookie()P: Sets a test cookie to determine whether the user's browser supports cookies. Due to the way cookies work, you won't be able to test this until the user's next page request. See Setting test cookies below for more information.

test_cookie_worked()P: Returns either True or False, depending on whether the user's browser accepted the test cookie. Due to the way cookies work, you'll have to call set_test_cookie() on a previous, separate page request. See Setting test cookies below for more information.

delete_test_cookie()P: Deletes the test cookie. Use this to clean up after yourself.

set_expiry(value)P

Sets the expiration time for the session. You can pass a number of different values:

If value is an integer, the session will expire after that many seconds of inactivity. For example, calling request.session.set_expiry(300) would make the session expire in 5 minutes.
If value is a datetime or timedelta object, the session will expire at that specific date/time. Note that datetime and timedelta values are only serializable if you are using the PickleSerializer.
If value is 0, the user's session cookie will expire when the user's Web browser is closed.
If value is None, the session reverts to using the global session expiry policy.

Reading a session is not considered activity for expiration purposes. Session expiration is computed from the last time the session was modified.

get_expiry_age()P

Returns the number of seconds until this session expires. For sessions with no custom expiration (or those set to expire at browser close), this will equal SESSION_COOKIE_AGE.

This function accepts two optional keyword arguments:

modification: last modification of the session, as a datetime object. Defaults to the current time.
expiry: expiry information for the session, as a datetime object, an int (in seconds), or None. Defaults to the value stored in the session by set_expiry(), if there is one, or None.

get_expiry_date()P

Returns the date this session will expire. For sessions with no custom expiration (or those set to expire at browser close), this will equal the date SESSION_COOKIE_AGE seconds from now.

This function accepts the same keyword arguments as get_expiry_age().

get_expire_at_browser_close()P: Returns either True or False, depending on whether the user's session cookie will expire when the user's Web browser is closed.

clear_expired()P: Removes expired sessions from the session store. This class method is called by clearsessions.

cycle_key()P: Creates a new session key while retaining the current session data. django.contrib.auth.login() calls this method to mitigate against session fixation.

Session serializationP

By default, Django serializes session data using JSON. You can use the SESSION_SERIALIZER setting to customize the session serialization format. Even with the caveats described in Write your own serializer, we highly recommend sticking with JSON serialization especially if you are using the cookie backend.

For example, here's an attack scenario if you use pickle to serialize session data. If you're using the signed cookie session backend and SECRET_KEY is known by an attacker (there isn't an inherent vulnerability in Django that would cause it to leak), the attacker could insert a string into their session which, when unpickled, executes arbitrary code on the server. The technique for doing so is simple and easily available on the internet. Although the cookie session storage signs the cookie-stored data to prevent tampering, a SECRET_KEY leak immediately escalates to a remote code execution vulnerability.

Bundled serializersP

class serializers.JSONSerializerP

A wrapper around the JSON serializer from django.core.signing. Can only serialize basic data types.

In addition, as JSON supports only string keys, note that using non-string keys in request.session won't work as expected:

>>> # initial assignment
>>> request.session[0] = 'bar'
>>> # subsequent requests following serialization & deserialization
>>> # of session data
>>> request.session[0]  # KeyError
>>> request.session['0']
'bar'

Similarly, data that can't be encoded in JSON, such as non-UTF8 bytes like '\xd9' (which raises UnicodeDecodeError), can't be stored.

See the Write your own serializer section for more details on limitations of JSON serialization.

class serializers.PickleSerializerP: Supports arbitrary Python objects, but, as described above, can lead to a remote code execution vulnerability if SECRET_KEY becomes known by an attacker.

Write your own serializerP

Note that unlike PickleSerializer, the JSONSerializer cannot handle arbitrary Python data types. As is often the case, there is a trade-off between convenience and security. If you wish to store more advanced data types including datetime and Decimal in JSON backed sessions, you will need to write a custom serializer (or convert such values to a JSON serializable object before storing them in request.session). While serializing these values is fairly straightforward (DjangoJSONEncoder may be helpful), writing a decoder that can reliably get back the same thing that you put in is more fragile. For example, you run the risk of returning a datetime that was actually a string that just happened to be in the same format chosen for datetimes).

Your serializer class must implement two methods, dumps(self, obj) and loads(self, data), to serialize and deserialize the dictionary of session data, respectively.

Session object guidelinesP

Use normal Python strings as dictionary keys on request.session. This is more of a convention than a hard-and-fast rule.
Session dictionary keys that begin with an underscore are reserved for internal use by Django.
Don't override request.session with a new object, and don't access or set its attributes. Use it like a Python dictionary.

示例P

This simplistic view sets a has_commented variable to True after a user posts a comment. It doesn't let a user post a comment more than once:

def post_comment(request, new_comment):
    if request.session.get('has_commented', False):
        return HttpResponse("You've already commented.")
    c = comments.Comment(comment=new_comment)
    c.save()
    request.session['has_commented'] = True
    return HttpResponse('Thanks for your comment!')

This simplistic view logs in a "member" of the site:

def login(request):
    m = Member.objects.get(username=request.POST['username'])
    if m.password == request.POST['password']:
        request.session['member_id'] = m.id
        return HttpResponse("You're logged in.")
    else:
        return HttpResponse("Your username and password didn't match.")

...And this one logs a member out, according to login() above:

def logout(request):
    try:
        del request.session['member_id']
    except KeyError:
        pass
    return HttpResponse("You're logged out.")

The standard django.contrib.auth.logout() function actually does a bit more than this to prevent inadvertent data leakage. It calls the flush() method of request.session. We are using this example as a demonstration of how to work with session objects, not as a full logout() implementation.

Setting test cookiesP

As a convenience, Django provides an easy way to test whether the user's browser accepts cookies. Just call the set_test_cookie() method of request.session in a view, and call test_cookie_worked() in a subsequent view -- not in the same view call.

This awkward split between set_test_cookie() and test_cookie_worked() is necessary due to the way cookies work. When you set a cookie, you can't actually tell whether a browser accepted it until the browser's next request.

It's good practice to use delete_test_cookie() to clean up after yourself. Do this after you've verified that the test cookie worked.

Here's a typical usage example:

from django.http import HttpResponse
from django.shortcuts import render

def login(request):
    if request.method == 'POST':
        if request.session.test_cookie_worked():
            request.session.delete_test_cookie()
            return HttpResponse("You're logged in.")
        else:
            return HttpResponse("Please enable cookies and try again.")
    request.session.set_test_cookie()
    return render(request, 'foo/login_form.html')

Using sessions out of viewsP

注解

The examples in this section import the SessionStore object directly from the django.contrib.sessions.backends.db backend. In your own code, you should consider importing SessionStore from the session engine designated by SESSION_ENGINE, as below:

>>> from importlib import import_module
>>> from django.conf import settings
>>> SessionStore = import_module(settings.SESSION_ENGINE).SessionStore

An API is available to manipulate session data outside of a view:

>>> from django.contrib.sessions.backends.db import SessionStore
>>> s = SessionStore()
>>> # stored as seconds since epoch since datetimes are not serializable in JSON.
>>> s['last_login'] = 1376587691
>>> s.create()
>>> s.session_key
'2b1189a188b44ad18c35e113ac6ceead'
>>> s = SessionStore(session_key='2b1189a188b44ad18c35e113ac6ceead')
>>> s['last_login']
1376587691

SessionStore.create() is designed to create a new session (i.e. one not loaded from the session store and with session_key=None). save() is designed to save an existing session (i.e. one loaded from the session store). Calling save() on a new session may also work but has a small chance of generating a session_key that collides with an existing one. create() calls save() and loops until an unused session_key is generated.

If you're using the django.contrib.sessions.backends.db backend, each session is just a normal Django model. The Session model is defined in django/contrib/sessions/models.py. Because it's a normal model, you can access sessions using the normal Django database API:

>>> from django.contrib.sessions.models import Session
>>> s = Session.objects.get(pk='2b1189a188b44ad18c35e113ac6ceead')
>>> s.expire_date
datetime.datetime(2005, 8, 20, 13, 35, 12)

Note that you'll need to call get_decoded() to get the session dictionary. This is necessary because the dictionary is stored in an encoded format:

>>> s.session_data
'KGRwMQpTJ19hdXRoX3VzZXJfaWQnCnAyCkkxCnMuMTExY2ZjODI2Yj...'
>>> s.get_decoded()
{'user_id': 42}

When sessions are savedP

By default, Django only saves to the session database when the session has been modified -- that is if any of its dictionary values have been assigned or deleted:

# Session is modified.
request.session['foo'] = 'bar'

# Session is modified.
del request.session['foo']

# Session is modified.
request.session['foo'] = {}

# Gotcha: Session is NOT modified, because this alters
# request.session['foo'] instead of request.session.
request.session['foo']['bar'] = 'baz'

In the last case of the above example, we can tell the session object explicitly that it has been modified by setting the modified attribute on the session object:

request.session.modified = True

To change this default behavior, set the SESSION_SAVE_EVERY_REQUEST setting to True. When set to True, Django will save the session to the database on every single request.

Note that the session cookie is only sent when a session has been created or modified. If SESSION_SAVE_EVERY_REQUEST is True, the session cookie will be sent on every request.

Similarly, the expires part of a session cookie is updated each time the session cookie is sent.

The session is not saved if the response's status code is 500.

Browser-length sessions vs. persistent sessionsP

You can control whether the session framework uses browser-length sessions vs. persistent sessions with the SESSION_EXPIRE_AT_BROWSER_CLOSE setting.

By default, SESSION_EXPIRE_AT_BROWSER_CLOSE is set to False, which means session cookies will be stored in users' browsers for as long as SESSION_COOKIE_AGE. Use this if you don't want people to have to log in every time they open a browser.

If SESSION_EXPIRE_AT_BROWSER_CLOSE is set to True, Django will use browser-length cookies -- cookies that expire as soon as the user closes their browser. Use this if you want people to have to log in every time they open a browser.

This setting is a global default and can be overwritten at a per-session level by explicitly calling the set_expiry() method of request.session as described above in using sessions in views.

注解

Some browsers (Chrome, for example) provide settings that allow users to continue browsing sessions after closing and re-opening the browser. In some cases, this can interfere with the SESSION_EXPIRE_AT_BROWSER_CLOSE setting and prevent sessions from expiring on browser close. Please be aware of this while testing Django applications which have the SESSION_EXPIRE_AT_BROWSER_CLOSE setting enabled.

Clearing the session storeP

As users create new sessions on your website, session data can accumulate in your session store. If you're using the database backend, the django_session database table will grow. If you're using the file backend, your temporary directory will contain an increasing number of files.

To understand this problem, consider what happens with the database backend. When a user logs in, Django adds a row to the django_session database table. Django updates this row each time the session data changes. If the user logs out manually, Django deletes the row. But if the user does not log out, the row never gets deleted. A similar process happens with the file backend.

Django does not provide automatic purging of expired sessions. Therefore, it's your job to purge expired sessions on a regular basis. Django provides a clean-up management command for this purpose: clearsessions. It's recommended to call this command on a regular basis, for example as a daily cron job.

Note that the cache backend isn't vulnerable to this problem, because caches automatically delete stale data. Neither is the cookie backend, because the session data is stored by the users' browsers.

SettingsP

A few Django settings give you control over session behavior:

Session securityP

Subdomains within a site are able to set cookies on the client for the whole domain. This makes session fixation possible if cookies are permitted from subdomains not controlled by trusted users.

For example, an attacker could log into good.example.com and get a valid session for their account. If the attacker has control over bad.example.com, they can use it to send their session key to you since a subdomain is permitted to set cookies on *.example.com. When you visit good.example.com, you'll be logged in as the attacker and might inadvertently enter your sensitive personal data (e.g. credit card info) into the attacker's account.

Another possible attack would be if good.example.com sets its SESSION_COOKIE_DOMAIN to "example.com" which would cause session cookies from that site to be sent to bad.example.com.

Technical detailsP

The session dictionary accepts any json serializable value when using JSONSerializer or any picklable Python object when using PickleSerializer. See the pickle module for more information.
Session data is stored in a database table named django_session .
Django only sends a cookie if it needs to. If you don't set any session data, it won't send a session cookie.

The `SessionStore` objectP

When working with sessions internally, Django uses a session store object from the corresponding session engine. By convention, the session store object class is named SessionStore and is located in the module designated by SESSION_ENGINE.

All SessionStore classes available in Django inherit from SessionBase and implement data manipulation methods, namely:

exists()
create()
save()
delete()
load()
clear_expired()

In order to build a custom session engine or to customize an existing one, you may create a new class inheriting from SessionBase or any other existing SessionStore class.

Extending most of the session engines is quite straightforward, but doing so with database-backed session engines generally requires some extra effort (see the next section for details).

Extending database-backed session enginesP

Creating a custom database-backed session engine built upon those included in Django (namely db and cached_db) may be done by inheriting AbstractBaseSession and either SessionStore class.

AbstractBaseSession and BaseSessionManager are importable from django.contrib.sessions.base_session so that they can be imported without including django.contrib.sessions in INSTALLED_APPS.

class base_session.AbstractBaseSessionP

抽象基本会话模型。

session_keyP: 主键。字段本身可能包含多达40个字符。当前实现生成一个32个字符的字符串（一个随机的数字序列和小写的ascii字母）。

session_dataP: 包含编码和序列化会话字典的字符串。

expire_dateP

指定会话何时到期的日期时间。

但是，过期的会话对用户不可用，但在运行 clearsessions 管理命令之前，它们仍可能存储在数据库中。

classmethod get_session_store_class()P: 返回要与此会话模型一起使用的会话存储类。

get_decoded()P

返回解码的会话数据。

解码由会话存储类执行。

还可以通过子类 BaseSessionManager 自定义模型管理器。

class base_session.BaseSessionManagerP

encode(session_dict)P

返回序列化并编码为字符串的给定会话字典。

编码由绑定到模型类的会话存储类执行。

save(session_key, session_dict, expire_date)P: 为提供的会话密钥保存会话数据，或在数据为空时删除会话。

通过重写以下描述的方法和属性，实现了 SessionStore 类的定制：

class backends.db.SessionStoreP

实现数据库支持的会话存储。

classmethod get_model_class()P: 如果需要的话，重写此方法以返回自定义会话模型。

create_model_instance(data)P

返回会话模型对象的新实例，该实例表示当前会话状态。

重写此方法提供了在将会话模型数据保存到数据库之前修改它的能力。

class backends.cached_db.SessionStoreP

实现缓存数据库支持的会话存储。

cache_key_prefixP: 添加到会话键中以生成缓存键字符串的前缀。

例如P

下面的示例显示了一个自定义数据库支持的会话引擎，它包括一个用于存储帐户id的附加数据库列（从而提供了一个选项，用于查询数据库中帐户的所有活动会话）：

from django.contrib.sessions.backends.db import SessionStore as DBStore
from django.contrib.sessions.base_session import AbstractBaseSession
from django.db import models

class CustomSession(AbstractBaseSession):
    account_id = models.IntegerField(null=True, db_index=True)

    @classmethod
    def get_session_store_class(cls):
        return SessionStore

class SessionStore(DBStore):
    @classmethod
    def get_model_class(cls):
        return CustomSession

    def create_model_instance(self, data):
        obj = super().create_model_instance(data)
        try:
            account_id = int(data.get('_auth_user_id'))
        except (ValueError, TypeError):
            account_id = None
        obj.account_id = account_id
        return obj

如果要从Django的内置` cached_db` 会话存储迁移到基于``cached_db`` 的自定义存储，则应重写缓存键前缀，以防止名称空间冲突：

class SessionStore(CachedDBStore):
    cache_key_prefix = 'mysessions.custom_cached_db_backend'

    # ...

URL中的会话IDP

Django会话框架完全是基于cookie的。正如PHP所做的那样，它不会回退到将会话ID放置在URL中作为最后的手段。这是一个有意设计的决定。这种行为不仅使URL变得很难看，而且使您的站点容易受到会话ID的盗用。

Django 2.2.5.dev20190823064900 文档

如何使用会话P

打开会话P

Configuring the session engineP

Using database-backed sessionsP

Using cached sessionsP

Using file-based sessionsP

Using sessions in viewsP

Session serializationP

Bundled serializersP

Write your own serializerP

Session object guidelinesP

示例P

Setting test cookiesP

Using sessions out of viewsP

When sessions are savedP

Browser-length sessions vs. persistent sessionsP

Clearing the session storeP

SettingsP

Session securityP

Technical detailsP

The `SessionStore` objectP

Extending database-backed session enginesP

例如P

URL中的会话IDP

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Django 2.2.5.dev20190823064900 文档

如何使用会话P

打开会话P

Configuring the session engineP

Using database-backed sessionsP

Using cached sessionsP

Using file-based sessionsP

Using cookie-based sessionsP

Using sessions in viewsP

Session serializationP

Bundled serializersP

Write your own serializerP

Session object guidelinesP

示例P

Setting test cookiesP

Using sessions out of viewsP

When sessions are savedP

Browser-length sessions vs. persistent sessionsP

Clearing the session storeP

SettingsP

Session securityP

Technical detailsP

The SessionStore objectP

Extending database-backed session enginesP

例如P

URL中的会话IDP

Last update:

The `SessionStore` objectP