StringBuffer对象比较(StringBuffer object comparision)

 经过大量搜索，我终于解决了我的问题。 因此，事实证明，如果您尝试对管理员中的M2M字段执行某些操作，则更改将由clear（）自动清除。 
 
 所以，我不得不建立一个新的模型管理类： 
 
class PostAdmin(admin.ModelAdmin):
    class Meta:
        model = Post

    def save_model(self, request, obj, form, change):
        print "from save_model"
        obj.save()

    def save_related(self, request, form, formsets, change):
        super(PostAdmin, self).save_related(request, form, formsets, change)
        obj = form.instance
        if obj.body:
            tag_list = [Tag.objects.get_or_create(name=word)[0] for word in obj.body.split() if word.startswith("#")]
            obj.tags.add(*tag_list)
            print("from save_related")
            obj.save()

admin.site.register(Post, PostAdmin)
 
 另外，我改变了我在制作标签列表的方式，因为@Prakhar从create()指向get_or_create() 。 注意 get_or_create（）期间的索引[0]，以获取实例而不是created实例。 
 
 signals.py： 
 
@receiver(post_save, sender=Post)
def create(sender, instance, **kwargs):
    if kwargs.get('created', True):
        tag_list = [Tag.objects.get_or_create(name=word)[0] for word in instance.body.split() if word.startswith("#")]
        print "from signals!: instance body: %s" % instance.body
        instance.tags.add(*tag_list)
    else:
        tag_list = [Tag.objects.get_or_create(name=word)[0] for word in instance.body.split() if word.startswith("#")]
        print "already signals!: instance body: %s" % instance.body
        instance.tags.add(*tag_list)

After searching a lot, I finally solved my problem. So, it turns out that if you try to do something to the M2M field in the admin, the change will get wiped out by the clear() automatically.
 
So, I had to make a new model admin class:
 
class PostAdmin(admin.ModelAdmin):
    class Meta:
        model = Post

    def save_model(self, request, obj, form, change):
        print "from save_model"
        obj.save()

    def save_related(self, request, form, formsets, change):
        super(PostAdmin, self).save_related(request, form, formsets, change)
        obj = form.instance
        if obj.body:
            tag_list = [Tag.objects.get_or_create(name=word)[0] for word in obj.body.split() if word.startswith("#")]
            obj.tags.add(*tag_list)
            print("from save_related")
            obj.save()

admin.site.register(Post, PostAdmin)
 
Also I changed how I was making list of tags as @Prakhar pointed out from create() to get_or_create(). Note the indexing [0] during get_or_create(), to get the instance and not the created.
 
signals.py:
 
@receiver(post_save, sender=Post)
def create(sender, instance, **kwargs):
    if kwargs.get('created', True):
        tag_list = [Tag.objects.get_or_create(name=word)[0] for word in instance.body.split() if word.startswith("#")]
        print "from signals!: instance body: %s" % instance.body
        instance.tags.add(*tag_list)
    else:
        tag_list = [Tag.objects.get_or_create(name=word)[0] for word in instance.body.split() if word.startswith("#")]
        print "already signals!: instance body: %s" % instance.body
        instance.tags.add(*tag_list)