添加一个“空”基于模型数据的 ChoiceField 选项
我正在根据模型的数据定义 ChoiceField。
field = forms.ChoiceField(choices=[[r.id, r.name] for r in Model.objects.all()])
不过，我想在我的选项前面添加一个空选项来选择“无”对象。 但我找不到一个好的方法来前置它。
我所有的测试都像：
field = forms.ChoiceField(choices=[[0, '----------']].extend([[r.id, r.name] for r in Model.objects.all()]))
返回“NoneType object not iterable”错误。 到目前为止我发现的唯一方法如下：
def append_empty(choices):
ret = [[0, '----------']]
for c in choices:
ret.append(c)
return ret
当我定义我的字段时：
forms.ChoiceField(choices=append_empty([[r.id, r.name] for r in
Restaurant.objects.all()]), required=False)
但是我想保持我的代码干净并且没有那种恐怖。 你能给我出个主意吗？ ：p 提前致谢。
I'm defining a ChoiceField based on a model's datas.
field = forms.ChoiceField(choices=[[r.id, r.name] for r in Model.objects.all()])
However I'd like to prepend my options with an empty one to select "no" objects.
But I can't find a nice way to prepend that.
All my tests like :
field = forms.ChoiceField(choices=[[0, '----------']].extend([[r.id, r.name] for r in Model.objects.all()]))
Returns me a "NoneType object not iterable" error.
The only way I've found until now is the following :
def append_empty(choices):
ret = [[0, '----------']]
for c in choices:
ret.append(c)
return ret
And when I define my field :
forms.ChoiceField(choices=append_empty([[r.id, r.name] for r in
Restaurant.objects.all()]), required=False)
However I'd like to keep my code clean and not have that kind of horrors.
Would you have an idea for me ? :p
Thanks by advance.
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一个简单的答案是：
不幸的是，你的方法是有缺陷的。即使使用您的“工作”方法，字段选择也是在定义表单时定义的，而不是在实例化表单时定义的 - 因此，如果您将元素添加到模型表中，它们将不会出现在选择列表中。
您可以通过在表单的 __init__ 方法中进行分配来避免这种情况。
然而，还有一种更简单的方法。您应该使用专门设计用于提供模型选择的字段 -
ModelChoiceField，而不是动态地搞乱字段选择。这不仅在实例化时动态获取模型元素列表，而且默认情况下它已经包含一个空白选择。请参阅文档。An easy answer is to do:
Unfortunately, your approach is flawed. Even with your 'working' approach, the field choices are defined when the form is defined, not when it is instantiated - so if you add elements to the Model table, they will not appear in the choices list.
You can avoid this by doing the allocation in the
__init__method of your Form.However, there is a much easier approach. Rather than messing about with field choices dynamically, you should use the field that is specifically designed to provide choices from a model -
ModelChoiceField. Not only does this get the list of model elements dynamically at instantiation, it already includes a blank choice by default. See the documentation.由于这个问题及其答案几乎解决了我刚刚遇到的问题，我想添加一些内容。对我来说，id 必须为空，因为模型无法将“0”识别为有效选项，但它接受空（null=True，blank=True）。在初始化程序中：
Since this question and its answer almost solved a problem I just had I'd like to add something. For me, the id had to be empty because the model didn't recognise '0' as a valid option, but it accepted empty (null=True, blank=True). In the initializer: