Django 表单模型选择框如何使用分组

起步

Django 表单中有两种字段类型可以使用选择框: ChoiceField 和 ModelChoiceField 。

对于 ChoiceField 的基本使用是:

class ExpenseForm(forms.Form):
    CHOICES = (
        (11, 'Credit Card'),
        (12, 'Student Loans'),
        (13, 'Taxes'),
        (21, 'Books'),
        (22, 'Games'),
        (31, 'Groceries'),
        (32, 'Restaurants'),
    )
    date = forms.DateField()
    category = forms.ChoiceField(choices=CHOICES)

它能渲染出:

使用分组下拉框

还可以使用如下方式生成 <optgourp> 标签：

class ExpenseForm(forms.Form):
    CHOICES = (
        ('Debt', (
            (11, 'Credit Card'),
            (12, 'Student Loans'),
            (13, 'Taxes'),
        )),
       ('Entertainment', (
            (21, 'Books'),
            (22, 'Games'),
        )),
        ('Everyday', (
            (31, 'Groceries'),
            (32, 'Restaurants'),
        )),
    )
    date = forms.DateField()
    category = forms.ChoiceField(choices=CHOICES)

能够渲染为：

分组模型下拉框

如果使用的是 ModelChoiceField ，那抱歉，Django本身没有提供解决方案。

在 https://code.djangoproject.com/ticket/27331 中提供了一个很好的解决方案。

首先为需要分类的类型创建模型，在另一个模型中用外键关联它：

from django.db import models

class Category(models.Model):
    name = models.CharField(max_length=30)
    parent = models.ForeignKey('Category', on_delete=models.CASCADE, null=True)

    def __str__(self):
        return self.name

class Expense(models.Model):
    amount = models.DecimalField(max_digits=10, decimal_places=2)
    date = models.DateField()
    category = models.ForeignKey(Category, on_delete=models.CASCADE)

    def __str__(self):
        return self.amount

其次，创建一个新的表单 Field 类型：

from functools import partial
from itertools import groupby
from operator import attrgetter

from django.forms.models import ModelChoiceIterator, ModelChoiceField

class GroupedModelChoiceIterator(ModelChoiceIterator):
    def __init__(self, field, groupby):
        self.groupby = groupby
        super().__init__(field)

    def __iter__(self):
        if self.field.empty_label is not None:
            yield ("", self.field.empty_label)
        queryset = self.queryset
        # Can't use iterator() when queryset uses prefetch_related()
        if not queryset._prefetch_related_lookups:
            queryset = queryset.iterator()
        for group, objs in groupby(queryset, self.groupby):
            yield (group, [self.choice(obj) for obj in objs])

class GroupedModelChoiceField(ModelChoiceField):
    def __init__(self, *args, choices_groupby, **kwargs):
        if isinstance(choices_groupby, str):
            choices_groupby = attrgetter(choices_groupby)
        elif not callable(choices_groupby):
            raise TypeError('choices_groupby must either be a str or a callable accepting a single argument')
        self.iterator = partial(GroupedModelChoiceIterator, groupby=choices_groupby)
        super().__init__(*args, **kwargs)

最后，在表单中可以如下进行使用：

from django import forms
from .fields import GroupedModelChoiceField
from .models import Category, Expense

class ExpenseForm(forms.ModelForm):
    category = GroupedModelChoiceField(
        queryset=Category.objects.exclude(parent=None), 
        choices_groupby='parent'
    )

    class Meta:
        model = Expense
        fields = ('amount', 'date', 'category')