检查数据库是否与 Null 字段重复答案

【问题标题】：Checking to see if a database duplicate with Null field检查数据库是否与 Null 字段重复
【发布时间】：2011-09-13 14:52:04
【问题描述】：

我正在尝试在添加条目之前检查并查看数据库中是否存在重复条目。这是我目前的模型--

class Education(models.Model):
    school = models.CharField(max_length=100)
    class_year = models.IntegerField(max_length=4, blank=True, null=True, choices=YEAR)
    degree = models.CharField(max_length=100, blank=True, null=True)

class UserProfile(models.Model):
    user = models.ForeignKey(User, unique=True)
    employments = models.ManyToManyField(Employment)

在表单上，用户必须输入学校。年级和学位是可选的。要检查重复条目，现在我有 --

if form.is_valid() and request.POST['school']:
    school = form.cleaned_data['school']
    try:
        school_object = Education.objects.get(school=form.cleaned_data['school'],
                                              class_year=form.cleaned_data['class_year'],
                                              degree = form.cleaned_data['degree'])
    except (Education.DoesNotExist):
        school_object = Education(school=form.cleaned_data['school'],
                                  class_year=form.cleaned_data['class_year'],
                                  degree = form.cleaned_data['degree'])
        school_object.save()
        profile.educations.add(school_object)
        profile.save()

如果未填写 class_date，我将收到 ValueError。如何解决这个问题以及检查重复项时？谢谢。

【问题讨论】：

标签： django django-models django-views

【解决方案1】：

首先，除非您有充分的理由，否则您真的不应该在不通过表单发送它们的情况下访问 post 变量。

from django import forms
class MyForm(forms.form):
  school = forms.CharField()
  degree = forms.CharField(required=False)
  class_year = forms.CharField(required=False)

  def clean(self):
    if not self.cleaned_data.has_key('degree'):
      self.cleaned_data['degree'] = None
    if not self.cleaned_data.has_key('class_year'):
      self.cleaned_data['class_year'] = None
    return self.cleaned_data

那么当你处理视图时：

...
if request.method == "POST":
  form = MyForm(request.POST)
  if form.is_valid():
    try:
      # NOTE that the objects.get method will raise MultipleObjectsReturned if the
      # database has more than one object that matches the query
      my_object = Education.objects.get(school=form.cleaned_data['school'], 
        class_year=form.cleaned_data['class_year'], 
        degree = form.cleaned_data['degree'])
    except Education.DoesNotExist:
      my_object = Education(school=form.cleaned_data['school'], 
        class_year=form.cleaned_data['class_year'], 
        degree = form.cleaned_data['degree'])
else:
  form = MyForm()
...

【讨论】：

这并不能解决 class_year 有 Null/None 字段的问题。它仍然会为基数为 10() 的无效文字创建 ValueError。还有其他想法吗？
我将 clean 方法更改为如下，现在可以使用：if not self.cleaned_data.get('class_year'):self.cleaned_data['class_year'] = Noneif not self.cleaned_data.get('degree'):self.cleaned_data['degree'] = ''return self.cleaned_data

【解决方案2】：

在视图中：

if 'Add School' in request.POST.values():
    form = EducationForm(request.POST)
    if form.is_valid() and request.POST['school']:
        school = form.cleaned_data['school']
        try:
            school_object = Education.objects.get(school=form.cleaned_data['school'],
                                              class_year=form.cleaned_data['class_year'],
                                              degree = form.cleaned_data['degree'])
        except (Education.DoesNotExist, ValueError):
            school_object = Education(school=form.cleaned_data['school'],
                                              class_year=form.cleaned_data['class_year'],
                                              degree = form.cleaned_data['degree'])
            school_object.save()
            profile.educations.add(school_object)
            profile.save()
            return redirect('edit_education')

或者，使用get_or_create 来简化：

if 'Add School' in request.POST.values():
    form = EducationForm(request.POST)
    if form.is_valid() and request.POST['school']:
        school = form.cleaned_data['school']
        school_object, created = Education.objects.get_or_create(school=form.cleaned_data['school'],
                                          class_year=form.cleaned_data['class_year'],
                                          degree = form.cleaned_data['degree'])
        if created:
            profile.educations.add(school_object)
            profile.save()
            return redirect('edit_education')

在表格中：

YEAR = ([(x, x) for x in range(1970,2015)])
YEAR.append((0,'Select Year'))
YEAR.reverse()

class EducationForm(forms.Form):
    school = forms.CharField()
    class_year = forms.ChoiceField(choices=YEAR, required=False)
    degree = forms.CharField(required=False)
    def clean(self):
        if not self.cleaned_data.get('class_year'):
            self.cleaned_data['class_year'] = None
        if not self.cleaned_data.get('degree'):
            self.cleaned_data['degree'] = ''
        return self.cleaned_data

【讨论】：