示例代码：
https://github.com/divio/djangocms-picture
以上一个图片的插件，安装后可在页面中添加图片，效果如下图：
以此为切入点，分析plugin的逻辑：
分析
1. plugin列表加载分析:
2. plugin实例添加到页面的分析：
通过DjDT分析得出，最终是交给了cms.admin.pageadmin.edit_plugin处理，如下：
而edit_plugin的代码非常简洁：
def edit_plugin(self, *args, **kwargs):
with create_revision():
return super(PageAdmin, self).edit_plugin(*args, **kwargs)
而PageAdmin的继承关系如下：
class PageAdmin(PlaceholderAdminMixin, ModelAdmin):
基本可以猜出，edit_plugin应该是mixin里面的函数，如下：
具体代码：
@xframe_options_sameorigin
def edit_plugin(self, request, plugin_id):
plugin_id = int(plugin_id)
cms_plugin = get_object_or_404(CMSPlugin.objects.select_related('placeholder'), pk=plugin_id)
instance, plugin_admin = cms_plugin.get_plugin_instance(self.admin_site)
if not self.has_change_plugin_permission(request, cms_plugin):
return HttpResponseForbidden(force_unicode(_("You do not have permission to edit this plugin")))
plugin_admin.cms_plugin_instance = cms_plugin
try:
plugin_admin.placeholder = cms_plugin.placeholder
except Placeholder.DoesNotExist:
pass
if request.method == "POST":
# set the continue flag, otherwise will plugin_admin make redirect to list
# view, which actually doesn't exists
request.POST['_continue'] = True
if request.POST.get("_cancel", False):
# cancel button was clicked
context = {
'CMS_MEDIA_URL': get_cms_setting('MEDIA_URL'),
'plugin': cms_plugin,
'is_popup': True,
"type": cms_plugin.get_plugin_name(),
'plugin_id': plugin_id,
'icon': force_escape(escapejs(cms_plugin.get_instance_icon_src())),
'alt': force_escape(escapejs(cms_plugin.get_instance_icon_alt())),
'cancel': True,
}
instance = cms_plugin.get_plugin_instance()[0]
if instance:
context['name'] = force_unicode(instance)
else:
# cancelled before any content was added to plugin
cms_plugin.delete()
context.update({
"deleted": True,
'name': force_unicode(cms_plugin),
})
return render_to_response('admin/cms/page/plugin/confirm_form.html', context, RequestContext(request))
if not instance:
# instance doesn't exist, call add view
response = plugin_admin.add_view(request)
else:
# already saved before, call change view
# we actually have the instance here, but since i won't override
# change_view method, is better if it will be loaded again, so
# just pass id to plugin_admin
response = plugin_admin.change_view(request, str(plugin_id))
if request.method == "POST" and plugin_admin.object_successfully_changed:
self.post_edit_plugin(request, plugin_admin.saved_object)
saved_object = plugin_admin.saved_object
context = {
'CMS_MEDIA_URL': get_cms_setting('MEDIA_URL'),
'plugin': saved_object,
'is_popup': True,
'name': force_unicode(saved_object),
"type": saved_object.get_plugin_name(),
'plugin_id': plugin_id,
'icon': force_escape(saved_object.get_instance_icon_src()),
'alt': force_escape(saved_object.get_instance_icon_alt()),
}
return render_to_response('admin/cms/page/plugin/confirm_form.html', context, RequestContext(request))
return response
经过调试发现，在
cms_plugin = get_object_or_404(CMSPlugin.objects.select_related('placeholder'), pk=plugin_id)
时plugin_id已经有值了，因此猜测，此id为plugin控件在控件表CMSPlugin中的id(CMSPlugin通过一个名为placeholder的字段m2m到Placeholder表，如下：)
@python_2_unicode_compatible class CMSPlugin(with_metaclass(PluginModelBase, MPTTModel)): ... placeholder = models.ForeignKey(Placeholder, editable=False, null=True)
placehoder似乎和plugin等价了，不过看不出玄机：
@python_2_unicode_compatible
class Placeholder(models.Model):
slot = models.CharField(_("slot"), max_length=50, db_index=True, editable=False)
default_width = models.PositiveSmallIntegerField(_("width"), null=True, editable=False)
cache_placeholder = True
...
def get_plugins_list(self, language=None):
return list(self.get_plugins(language))
def get_plugins(self, language=None):
if language:
return self.cmsplugin_set.filter(language=language).order_by('tree_id', 'lft')
else:
return self.cmsplugin_set.all().order_by('tree_id', 'lft')
回到正题：
instance, plugin_admin = cms_plugin.get_plugin_instance(self.admin_site)
新建时,instance为None，plugin_admin为PicturePlugin的实例。分析源码，得出，plugin是从控件池中取出来的，如下：
def get_plugin_class(self):
from cms.plugin_pool import plugin_pool
return plugin_pool.get_plugin(self.plugin_type)
def get_plugin_class_instance(self, admin=None):
plugin_class = self.get_plugin_class()
# needed so we have the same signature as the original ModelAdmin
return plugin_class(plugin_class.model, admin)
def get_plugin_instance(self, admin=None):
plugin = self.get_plugin_class_instance(admin)
if hasattr(self, "_inst"):
return self._inst, plugin
if plugin.model != self.__class__: # and self.__class__ == CMSPlugin:
# (if self is actually a subclass, getattr below would break)
try:
instance = plugin.model.objects.get(cmsplugin_ptr=self)
instance._render_meta = self._render_meta
except (AttributeError, ObjectDoesNotExist):
instance = None
else:
instance = self
self._inst = instance
return self._inst, plugin
最终，由于instance为空，进入以下逻辑：
if not instance:
# instance doesn't exist, call add view
response = plugin_admin.add_view(request)
此处分析也有些力不从心（后续深入）
=============
经过以上分析，plugin列表的加载逻辑已经呼之欲出了，留给细心的读者自己发掘。
总结：
1. 控件加载用到的类：
CMSPlugin/PlaceholderAdminMixin/Placeholder/PageAdmin/Page等，继承关系如下：
2. 当在页面中添加plugin时，调用关系：
1). PageAdmin.edit_plugin
2). PlaceholderAdminMixin.edit_plugin ， 其处理逻辑是：
a). 首先通过CMSPlugin得到一个cms_plugin对象。
b). 通过cms_plugin对象得到控件实例instance和plugin_admin，其中plugin_admin是重插件池 plugin_pool中根据类型得到的。
c). 如果实例为空(新建),通过plugin_admin的add_view方法返回一个response对象，否则（编辑），通过change_view方法返回response对象。
d). 如果请求方式是Post,并且plugin_admin的object_successfully_changed为真值，则给予相关提示信息。