使用Djongo连接MongoDB时Django Admin嵌入字段报错求助

报错原因 #

报错Value: gwalior-MP-India must be an instance of <class 'dict'>的核心问题是：Django Admin默认将City模型的__str__返回值（字符串格式的城市信息）作为city字段的提交值，但Djongo的EmbeddedField要求传入的是字典类型（对应MongoDB的嵌入文档）或者City模型实例，字符串类型不匹配导致保存失败。

解决方案 #

根据业务需求，分两种场景处理：

场景1：添加Address时直接输入新的城市信息 #

自定义Admin表单，为嵌入的City字段拆分成单独的输入框，提交时自动组装成EmbeddedField需要的字典格式：

修改admin.py：

from django.contrib import admin
from django import forms
from .models import City, Address

class CityAdmin(admin.ModelAdmin):
    list_display = ['city', 'state', 'country']

class AddressAdminForm(forms.ModelForm):
    # 拆分嵌入字段的输入项
    city_name = forms.CharField(max_length=255, required=False, label='城市')
    state_name = forms.CharField(max_length=255, required=False, label='省份/邦')
    country_name = forms.CharField(max_length=255, required=False, label='国家')

    class Meta:
        model = Address
        fields = ['city_name', 'state_name', 'country_name', 'pincode']

    def save(self, commit=True):
        instance = super().save(commit=False)
        # 将输入的城市信息组装成字典赋值给EmbeddedField
        if self.cleaned_data.get('city_name'):
            instance.city = {
                'city': self.cleaned_data['city_name'],
                'state': self.cleaned_data['state_name'],
                'country': self.cleaned_data['country_name']
            }
        if commit:
            instance.save()
        return instance

class AddressAdmin(admin.ModelAdmin):
    form = AddressAdminForm
    list_display = ['get_city', 'pincode']

    # 自定义列表页显示城市信息的方法
    def get_city(self, obj):
        if obj.city:
            return f"{obj.city.get('city')}-{obj.city.get('state')}-{obj.city.get('country')}"
        return '-'
    get_city.short_description = '城市信息'

admin.site.register(City, CityAdmin)
admin.site.register(Address, AddressAdmin)

场景2：选择已创建的City实例嵌入到Address中 #

如果希望复用已有的City数据，自定义表单让用户选择已创建的City，提交时将实例数据转换成字典：

修改admin.py：

from django.contrib import admin
from django import forms
from .models import City, Address

class CityAdmin(admin.ModelAdmin):
    list_display = ['city', 'state', 'country']

class AddressAdminForm(forms.ModelForm):
    # 添加下拉选择框选择已有City
    selected_city = forms.ModelChoiceField(queryset=City.objects.all(), required=False, label='选择已有城市')

    class Meta:
        model = Address
        fields = ['selected_city', 'pincode']

    def save(self, commit=True):
        instance = super().save(commit=False)
        # 将选中的City实例数据转换成字典
        if self.cleaned_data.get('selected_city'):
            city_obj = self.cleaned_data['selected_city']
            instance.city = {
                'city': city_obj.city,
                'state': city_obj.state,
                'country': city_obj.country
            }
        if commit:
            instance.save()
        return instance

class AddressAdmin(admin.ModelAdmin):
    form = AddressAdminForm
    list_display = ['get_city', 'pincode']

    def get_city(self, obj):
        if obj.city:
            return f"{obj.city.get('city')}-{obj.city.get('state')}-{obj.city.get('country')}"
        return '-'
    get_city.short_description = '城市信息'

admin.site.register(City, CityAdmin)
admin.site.register(Address, AddressAdmin)

补充说明 #

• 原City模型中的_id字段可以保留，嵌入时无需手动传入，MongoDB会自动为嵌入文档生成_id（如果不需要可以删除该字段）。
• 测试时先创建几个City实例，再操作Address的添加，即可正常保存数据。

内容的提问来源于stack exchange，提问作者Abhishek Jain