使用 ModelForms 时如何更新已存在的行？

Question

我有一个问题，当其中一个字段是我的主键时，如何更新数据库中的现有行。我正在使用 ModelForm 和 Django-Piston - 我的主要目标是将 RESTful Post 发送到我的网络服务。我能够正确发送初始帖子（即主键值尚不存在）。问题是当我想更新主键已存在的值时 - 当我发出 f.is_valid() 时它会失败，因为“此 UniqueIdentifier 已存在”。如何使用 ModelForms 进行表单验证以更新现有行？

models.py：forms.py

from django.db import models
class DeviceModel(models.Model):
    uniqueIdentifier = models.CharField(primary_key=True, max_length=100)
    deviceToken = models.CharField(max_length=100)

我的

from django import forms
from models import DeviceModel
class DeviceModelForm(forms.ModelForm):
    class Meta:
        model = DeviceModel

handlers.py

class DeviceHandler(BaseHandler):
allowed_methods = ('POST', 'GET', 'DELETE',)
def create(self, request):
    f = DeviceModelForm(request.POST)
    if f.is_valid():
        new_object = f.save()
        return new_object
    return rc.BAD_REQUEST

urls.py

from django.conf.urls.defaults import *
from piston.resource import Resource
from api.handlers import DeviceHandler

device_handler = Resource(DeviceHandler)

urlpatterns = patterns('',
    (r'^api/$', device_handler, {'emitter_format': 'json'}),
)

Answer 1

django 文档 给出了如何创建“表单”的简单示例更改现有的 [[entity]]”：

>>> article = Article.objects.get(pk=1)
>>> form = ArticleForm(instance=article)

如果您想使用相同的流程来插入新对象和更改现有对象，则必须根据查找主键是否成功来单独实例化表单（现有对象）或失败（新对象）！-)

Answer 2

要更新现有行（或 ORM 中的对象），您必须告诉 ModelForm 在实例化它时使用什么实例：

f = DeviceModelForm(request.POST, instance=myobject)

我不确定您从哪里获得 myobject > 虽然使用活塞，但你的问题似乎暗示你已经解决了这个特定问题。

Answer 3

这是一个更完整的解决方案，不使用任何基于类的视图，汇集了此页面上的其他答案和评论。

我把它作为对 jquery ajax 的回复。

def save_product(request):                                                                       
    if request.method == "POST":                                                                 
        # first get the model pk we are looking for
        postpk = request.POST.get('pk', None)

        # get the model from the db                                                
        model, created = Product.objects.get_or_create(pk = postpk)                          

        # create the from based on the model, but with the 
        # request data overriding the model data                                                 
        form = ProductForm(request.POST, instance = model)

        # save if valid                                       
        if form.is_valid():                                                                      
            form.save()                                                                          
            return HttpResponse("saved")                                         
        else:                             
            # will go to the the ajax error: data.responseText                                                       
            return HttpResponseNotFound("%s" % (form.errors))                                    
    else:                                                                                        
        return HttpResponseNotFound('eh? this was not a Post?')   

Answer 4

这是我根据实体是否存在进行更新或创建的操作：

# first see the DeviceModel exists and should simply be updated

try:
    instance = DeviceModel.objects.get(mycolumn=data['mycolumn'])
    f = DeviceModelForm(data, instance=instance)
except DeviceModel.DoesNotExist:
    # DeviceModel doesn't exists, so we create a new one
    f = DeviceModelForm(data)
except DeviceModel.MultipleObjectsReturned:
    # our query found multiple DeviceModel
    # either update them all or throw an error
    print("Found multiple DeviceModels")

if f.is_valid():
    f.save()