Django 保存选择值

Question

I want to save selected choice in model. And I want to use Select widget for choices. I have a model:

qobj = Model1.objects.all()

CHOICE = (
    (x.id, x.name) for x in qobj
)

class Model2(models.Model):
    choice_field = models.CharField("CHOICE", max_length=77, choices=CHOICE)

And I got error: "Select a valid choice. 5 is not one of the available choices." - error when try to save. I was try forms.ModelChoiceField(queryset=qobj) - No Problem, but I can't get Model.get_choice_field_display() . May be someone know solving of this problem?

Answer 1

Error is here:

date = MyModel.objects.order_by('date')[0]
name = MyModel.objects.order_by('name')[0]

MyModel.objects.order_by('date') return a QuerySet, if queryset is empty, it has no index '[0]'. Try 'first()' instead [0]:

date = MyModel.objects.order_by('date').first()
name = MyModel.objects.order_by('name').first()

Case MyModel is empty, first return None Docs: https://docs.djangoproject.com/en/1.9/ref/models/querysets/#first

Answer 2

The issue is caused here:

def preview(request):
    form = MyModelForm()
    date = MyModel.objects.order_by('date')[0]
    name = MyModel.objects.order_by('name')[0]

You are querying objects, sorting and taking the first item. However, if there are no items it is not possible to do this. Instead use .first() , eg

    date = MyModel.objects.order_by('date').first()
    name = MyModel.objects.order_by('name').first()

This will return the first item, if there is one, or None if not. See the documentation for more info. There are also some other examples in this question for alternative ways to handle this.

However, I would recommend that you do not use this approach . When you save the new object ( form01.save() ) this returns the newly created object. You can then access this directly for your preview. For example:

preview_model = form01.save()

Using MyModel.objects.order_by('date').first() to get the 'latest record' opens you to a race condition when another user edits another object between the .save() and the select.

I'm not sure of the purpose of name = MyModel.objects.order_by('name').first() as this is going to return a completely different object to the previous bit (the first object sorted alphabetically ) - and I cannot imagine why you would want that. Try something like the following in views.py :

def form1(request):
    form = MyModelForm()
    if request.method == 'POST':
        form01 = MyModelForm(request.POST, request.FILES)
        if form01.is_valid():
           preview = form01.save()
           date = preview.date
           return render(request, 'WebMamOffice/en/preview.html', {'form': form01, 'date': date, 'name': name})
    return render(request, 'WebMamOffice/en/form1.html', {'form': form})

Answer 3

您的preview()视图假定至少存在MyModel一个实例：您正在访问MyModel.objects.blah[0] ，它仅在[0]处有内容时才有效。

Answer 4

The best way to use ManyToManyField:

class Model2(models.Model):
    choice_field = models.ManyToManyField(to=Model1)

Answer 5

在django中部分解决了这个问题无法保存模型选择选定值