django-cms 代码研究（八）app hooks

app钩子，啥玩意呢？

就是把现有的app，集成到cms的一种手段。

有两种实现方式：

1) 定义cms_app.py，如下：

from cms.app_base import CMSApp
from cms.apphook_pool import apphook_pool
from django.utils.translation import ugettext_lazy as _

class MyApphook(CMSApp):
    name = _("My Apphook")
    urls = ["myapp.urls"]

apphook_pool.register(MyApphook)

官方文档查看这里：http://docs.django-cms.org/en/latest/extending_cms/app_integration.html#app-hooks

加载逻辑，通过discover_apps的load('cms_app')来加载(前提是在settings.py中未定义 CMS_APPHOOKS):在所有的installed_app中，查找cms_app模块，并自动import_module

2) 在setting.py中定义CMS_APPHOOKS

APPHOOKS=(
'yourmodule.you_object1','yourmodule.you_object2',...
)

这是从源码中分析的来的，如下：

C:\Python27\Lib\site-packages\django_cms-3.0.3-py2.7.egg\cms\apphook_pool.py (45~57)

    def discover_apps(self):
        self.apphooks = get_cms_setting('APPHOOKS')

        if self.apphooks:
            for cls in iterload_objects(self.apphooks):
                try:
                    self.register(cls, discovering_apps=True)
                except AppAlreadyRegistered:
                    pass

        else:
            load('cms_app')

        self.discovered = True

iterload_objects,是一个生成器，如下：

def iterload_objects(import_paths):
    """
    Load a list of objects.
    """
    for import_path in import_paths:
        yield load_object(import_path)

load_object

def load_object(import_path):
    if '.' not in import_path:
        raise TypeError(
            "'import_path' argument to 'django_load.core.load_object' must "
            "contain at least one dot."
        )
    module_name, object_name = import_path.rsplit('.', 1)
    module = import_module(module_name)
    return getattr(module, object_name)

顺便分析下　C:\Python27\Lib\site-packages\django_cms-3.0.3-py2.7.egg\cms\apphook_pool.py的源码：

实例变量：

    def __init__(self):
        self.apphooks = []
        self.apps = {}
        self.discovered = False

方法：clear/register/discover_apps/get_apphooks/get_apphook

其中： discover_apps上面已经分析过了。

clear，清空实例变量，如下（作者说，python不需要clear，会自动回收，这个方法该砍掉了）：

    def clear(self):
        # TODO: remove this method, it's Python, we don't need it.
        self.apphooks = []
        self.apps = {}
        self.discovered = False

register，用于注册app，app的基类如下：

class CMSApp(object):
    name = None
    urls = None
    menus = []
    app_name = None
    permissions = True

register，本质是把app放到apphook_pool实例的apps中，不过之前会有一些验证，如下：

    def register(self, app, discovering_apps=False):
        if self.apphooks and not discovering_apps:
            return

        if app.__name__ in self.apps:
            raise AppAlreadyRegistered(
                'A CMS application %r is already registered' % app.__name__)

        if not issubclass(app, CMSApp):
            raise ImproperlyConfigured(
                'CMS application must inherit from cms.app_base.CMSApp, '
                'but %r does not' % app.__name__)

        if not hasattr(app, 'menus') and hasattr(app, 'menu'):
            warnings.warn("You define a 'menu' attribute on CMS application %r, "
                "but the 'menus' attribute is empty, did you make a typo?" % app.__name__)

        self.apps[app.__name__] = app

其干活的代码只有最后一句：

self.apps[app.__name__] = app

get_apphooks， 返回一个列表 [(app,app.name)....],并按照app.name排序，如下：

    def get_apphooks(self):
        hooks = []

        if not self.discovered:
            self.discover_apps()

        for app_name in self.apps:
            app = self.apps[app_name]

            if app.urls:
                hooks.append((app_name, app.name))

        # Unfortunately, we loose the ordering since we now have a list of tuples. Let's reorder by app_name:
        hooks = sorted(hooks, key=lambda hook: hook[1])

        return hooks

get_apphook,根据app名字查找app，代码如下：

    def get_apphook(self, app_name):
        if not self.discovered:
            self.discover_apps()

        try:
            return self.apps[app_name]
        except KeyError:
            # deprecated: return apphooks registered in db with urlconf name instead of apphook class name
            for app in self.apps.values():
                if app_name in app.urls:
                    return app

        raise ImproperlyConfigured('No registered apphook %r found' % app_name)