django-cms 代码研究（六）plugin的深入分析

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。