Django多对多字段赋值报错：禁止直接赋值，请使用set()替代

报错信息：

Direct assignment to the forward side of a many-to-many set is prohibited. Use user.set() instead

我的代码：

models.py #

class Display(models.Model):
    url = models.URLField(unique=True)
    text = models.CharField(max_length=150) 
    
class Display_Data(models.Model):
    displays = models.ManyToManyField(Display)  
    user = models.ManyToManyField(User)
    choosenum = models.IntegerField()
    puplish_date = models.DateTimeField(default=datetime.now)

views.py #

def submit_operation(request):
 if request.method == 'POST':
    url = request.POST.get('url')
    text = request.POST.get('title')
    choosenum = request.POST.get('CHOOSE')

    if Display.objects.filter(url=url).exists():
        display = Display.objects.get(url=url)
        display_data = Display_Data.objects.create(choosenum=choosenum, user=request.user, date_published=datetime.now())
        display_data.displays.add(display)
    else:
        display = Display.objects.create(url=url, text=text)
        display_data = Display_Data.objects.create(choosenum=choosenum, user=request.user, date_published=datetime.now())
        display_data.displays.add(display)        

    return redirect(request.META.get('HTTP_REFERER'))

问题原因 #

报错核心原因是Display_Data里的user是多对多字段，Django不允许在create()方法中直接给多对多字段赋值，必须先创建对象，再通过add()或set()方法关联多对多关系。另外原代码中模型字段是puplish_date，但创建时写了date_published，这也会导致字段不存在的报错。

修复后的代码 #

修改views.py的创建逻辑，拆分多对多字段的关联步骤：

def submit_operation(request):
 if request.method == 'POST':
    url = request.POST.get('url')
    text = request.POST.get('title')
    choosenum = request.POST.get('CHOOSE')

    if Display.objects.filter(url=url).exists():
        display = Display.objects.get(url=url)
        # 先创建Display_Data实例，不传入user参数
        display_data = Display_Data.objects.create(choosenum=choosenum, puplish_date=datetime.now())
        display_data.displays.add(display)
        # 单独添加用户关联
        display_data.user.add(request.user)
    else:
        display = Display.objects.create(url=url, text=text)
        # 先创建Display_Data实例，不传入user参数
        display_data = Display_Data.objects.create(choosenum=choosenum, puplish_date=datetime.now())
        display_data.displays.add(display)        
        # 单独添加用户关联
        display_data.user.add(request.user)

    return redirect(request.META.get('HTTP_REFERER'))

内容的提问来源于stack exchange，提问作者mohamed sadik