django save_model() 错误创建具有 m2m 字段的新对象

Question

我有一个模型 models.py :

class MyModelClass(models.Model):
    name  = models.CharField(max_length=255)
    m2m_1 = models.ManyToManyField(A, blank=True, null=True)     
    m2m_2 = models.ManyToManyField(B, blank=True, null=True) 
    fk    = models.ForeignKey('C')
    int   = models.IntegerField()   

和一个 admin.py类(class):

class MyModelClassAdmin(admin.ModelAdmin):
    list_display = ('name',)

    #Get all fields selected in MyModelClass m2m_2
    def get_selected_in_m2m_2(self, obj):
        sel = obj.m2m_2.all() #This line is the one for i get an error. The error is described below.
        return sel

    def save_model(self, request, obj, form, change):
        """When creating a new object, set the creator field.
        """
        m2m_2_selected = self.get_selected_in_m2m_2(obj)
        print m2m_2_selected

        print request.user
        if not change:
            obj.creator = request.user
        obj.save()

问题:
如果我已经单击“保存”按钮，一切正常 现有 我的管理页面中的 MyModelClass 对象。
但如果我尝试 创建 在管理页面中创建一个新模型对象并单击“保存”按钮(保存新对象，而不是更新现有对象)，我会收到错误: 'MyModelClass' instance needs to have a primary key value before a many-to-many relationship can be used.
对不起我的英语不好。
任何帮助表示赞赏。
谢谢。

Answer 1

def save_model(self, request, obj, form, change):
    """When creating a new object, set the creator field.
    """
    if not change:
        obj.creator = request.user

    super(MyModelClassAdmin, self).save_model(request, obj, form, change)

    m2m_2_selected = self.get_selected_in_m2m_2(obj)
    print m2m_2_selected
    print request.user