在"添加窗体"上向自引用外键添加选项"self"

Question

我有一个自引用的ForeignKey字段:

class Thing(models.Model)
    special_thing = models.ForeignKey(
        'self',
        blank=True,
        null=True
    )

在"Add Thing"表单中，除了其他已经存在的东西之外，我还需要提供一个选项"this Thing本身"，即尚未添加的东西。告诉用户添加然后重新访问该字段不是一个选项。

我该怎么做呢?

我现在的想法是重写表单:

• 将"special_thing"从默认的ModelChoiceField更改为ChoiceField
• 在__init__()
中为字段的选项添加新的特殊("marker")选项"*** THIS THING ***"
• 提供clean_special_thing()，允许"*** THIS THING ***"或可以从查询集中查找的THING的id。
• 在save()中，如果选择"*** THIS THING ***"，则使用special_thing=None保存THING，然后将其设置为自身并再次保存。否则，根据给定的id查找Thing并像往常一样保存。

我正在为ModelAdmin的ModelForm做这件事。有更简单的方法吗?

Answer 1

另一个可能的解决方案是使用jQuery(示例)在模板内的表单字段中添加另一个***THIS THING***。

提交表单后，您可以在表单的clean -方法或视图中检查所选选项以存储它。

例如:

if request.POST:
    if request.POST['special_thing'] == 'myself':
        # do whatever should be done
        ...

Answer 2

我已经按照这些想法进行了，最后一步是不必要的。相反，clean方法可以将选择设置为表单的实例，并且总体工作仍然非常合理:

from django.contrib import admin
from django import forms
from mdoels import Thing
MARKER_THIS_THING = '*** THIS THING ***'

class ThingAdmin(admin.ModelAdmin):
    def get_form(self, request, obj=None, **kwargs):
        """
        Return the Thing ModelForm with an additional choice for the
        'special_thing' field (FK to self) that allows the Add Thing form
        to refer to the newly added instance itself.
        """
        form = super(ThingAdmin, self).get_form(request, obj, **kwargs)
        # The form still has a ModelChoiceField for special_thing, construct
        # new non-model choices from that so we can add the 'this thing' choice
        thing_choices = [c for c in form.base_fields['special_thing'].choices]
        if not obj:
            # Only the Add form needs the special choice
            thing_choices = [(MARKER_THIS_THING, MARKER_THIS_THING)] + thing_choices
        form.base_fields['special_thing'] = forms.ChoiceField(
            choices=thing_choices
        )
        def clean_special_thing(form):
            """
            Now just a simple ChoiceField, convert posted values to
            model instances like a ModelChoiceField does.
            Convert special new 'this thing' choice to be the newly added
            instance.
            """
            data = form.cleaned_data['special_thing']
            instance = getattr(form, 'instance', None)
            if data==MARKER_THIS_THING and not (instance and instance.pk):
                # Referring to new instance itself on Add form
                return instance
            # Return selected model like a ModelChoiceField does
            try:
                data = Thing.objects.get(pk=data)
            except Thing.DoesNotExist:
                raise forms.ValidationError('Invalid choice')
            return data
        # clean_* are not part of ModelAdmin, just of forms and models.
        # So we attach it to the form:
        form.clean_special_thing = clean_special_thing
        return form