Django Admin - save_model方法 - 如何检测字段是否已更改？ [英] Django Admin - save_model method - How to detect if a field has changed?

问题描述

我试图覆盖 save_model方法在Django管理对象，以防止用户更改某个字段。然而，我找不到一个方法来确定这个方法是否已经改变了。

I'm trying to override the save_model method on a Django admin object to prevent a user from changing a certain field. However I can't find a way to find out if the field has changed within this method.

这是我的代码到目前为止：

Here's my code so far:

def save_model(self, request, obj, form, change):
    if change: 
        if obj.parking_location == form.cleaned_data['parking_location']:
            super(MyVehiclesAdmin, self).save_model(request, obj, form, change)
        else:
            messages.error(request, 
                "The Parking Location field cannot be changed.")

问题是obj.parking_location和form.cleaned_data [' parking_location']具有新值。 （这可能是Django中的一个bug吗？好像obj应该包含预先保存的值）。在任何情况下，是否有另一种方法来实现？

The problem is both obj.parking_location, and form.cleaned_data['parking_location'] have the new value. (Could this be a bug in Django? It really seems like the obj should contain the pre-save values). In any case, is there another way to accomplish this?

（我在Django 1.2上）

(I'm on Django 1.2)

推荐答案

首先，这不是一个bug，它是Django 1.2起的记录行为。

Firstly, this isn't a bug, it's the documented behaviour in Django 1.2 onwards.

从 Django 1.2发行说明：

第一次调用 ModelForm.is_valid（），访问 ModelForm.errors 或以其他方式触发表单验证，您的模型将被原位清理。此转换用于在保存模型时发生。如果您需要一个未修改的模型实例，则应将一个副本传递给ModelForm构造函数。

the first time you call ModelForm.is_valid(), access ModelForm.errors or otherwise trigger form validation, your model will be cleaned in-place. This conversion used to happen when the model was saved. If you need an unmodified instance of your model, you should pass a copy to the ModelForm constructor.

如果要防止用户从编辑一个关键字段，更好的方法可能是使用 ModelAdmin.readonly_fields 选项。

If you want to prevent the user from editing a paticular field, a better approach might be to use the ModelAdmin.readonly_fields option.

class VehicleRegistrationAdmin(admin.ModelAdmin):
    readonly_fields = ('parking_location',)

或者，你可以将 ModelAdmin.form 替换为排除该字段的自定义表单。

Or, you could replace the ModelAdmin.form with a custom form that excludes that field.

class VehicleRegistrationForm(forms.ModelForm):
    class Meta:
        exclude = ('parking_location',)

class VehicleRegistrationAdmin(ModelAdmin):
    form = VehicleRegistrationForm

最后，直接回答你的问题，你c通过检查 form.changed_data 来检查 save_model 方法中字段是否已更改。这是一个更改字段名称的列表。

Finally, to answer your question more directly, you can check whether a field has changed in the save_model method by inspecting form.changed_data. This is a list of the names of the fields which have changed.

def save_model(self, request, obj, form, change):
    if 'parking_location' in form.changed_data:
        messages.info(request, "Parking location has changed")
    else:
        messages.info(request, "Parking location has not changed")
    super(MyVehiclesAdmin, self).save_model(request, obj, form, change)

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