Django：如何从模型中验证 unique_together

Question

我有以下几点：

class AccountAdmin(models.Model):

    account = models.ForeignKey(Account)
    is_master = models.BooleanField()
    name = models.CharField(max_length=255)
    email = models.EmailField()

    class Meta:
        unique_together = (('Account', 'is_master'), ('Account', 'username'),)

如果我随后在同一个帐户上创建一个与另一个用户名相同的新 AccountAdmin，而不是在模板中显示一个错误，它会因 IntegrityError 而中断并且页面消失。我希望在我看来，我可以去：

if new_accountadmin_form.is_valid():
    new_accountadmin_form.save()

我该如何解决这个问题。是否有第二种 is_valid() 类型的方法来检查 DB 是否违反了 unique_together = (('Account', 'is_master'), ('Account', 'username'),) 部分？

我不想在我的视图中捕获 IntegrityError。那是域逻辑与表示逻辑的混合。它违反了 DRY，因为如果我在 2 页上显示相同的表格，我将不得不重复相同的块。它也违反了 DRY，因为如果我对同一事物有两种形式，我必须写相同的 except: 再次。

Answer 1

有两种选择：

a) 使用 try 块保存模型并捕获 IntegrityError 并进行处理。比如：

try:
    new_accountadmin_form.save()
except IntegrityError:
    new_accountadmin_form._errors["account"] = ["some message"]
    new_accountadmin_form._errors["is_master"] = ["some message"]

    del new_accountadmin_form.cleaned_data["account"]
    del new_accountadmin_form.cleaned_data["is_master"]

b) 在表单的 clean() 方法中，检查 a 行是否存在并使用适当的消息引发 forms.ValidationError。示例here。

---

所以，b) 它是...这就是为什么我referenced the documentation; all you need is there.

但它会是这样的：

class YouForm(forms.Form):
    # Everything as before.
    ...

    def clean(self):
       """ This is the form's clean method, not a particular field's clean method """
       cleaned_data = self.cleaned_data

       account = cleaned_data.get("account")
       is_master = cleaned_data.get("is_master")
       username = cleaned_data.get("username")

       if AccountAdmin.objects.filter(account=account, is_master=is_master).count() > 0:
           del cleaned_data["account"]
           del cleaned_data["is_master"]
           raise forms.ValidationError("Account and is_master combination already exists.")

       if AccountAdmin.objects.filter(account=account, username=username).count() > 0:
           del cleaned_data["account"]
           del cleaned_data["username"]
           raise forms.ValidationError("Account and username combination already exists.")

    # Always return the full collection of cleaned data.
    return cleaned_data

对于它的价值 - 我刚刚意识到您上面的 unique_together 引用了一个名为 username 的字段，该字段未在模型中表示。

在调用各个字段的所有 clean 方法之后调用上面的 clean 方法。

Answer 2

对于一个完全通用的方式。在模型中有如下两个helper fns：

def getField(self,fieldName):
  # return the actual field (not the db representation of the field)
  try:
    return self._meta.get_field_by_name(fieldName)[0]
  except models.fields.FieldDoesNotExist:
    return None

和

def getUniqueTogether(self):
  # returns the set of fields (their names) that must be unique_together
  # otherwise returns None
  unique_together = self._meta.unique_together
  for field_set in unique_together:
    return field_set
  return None

并且在表格中有以下fn：

def clean(self):
  cleaned_data = self.cleaned_data
  instance = self.instance

  # work out which fields are unique_together
  unique_filter = {}
  unique_fields = instance.getUniqueTogether()
  if unique_fields:
    for unique_field in unique_fields:
      field = instance.getField(unique_field)
      if field.editable: 
        # this field shows up in the form,
        # so get the value from the form
        unique_filter[unique_field] = cleaned_data[unique_field]
      else: 
        # this field is excluded from the form,
        # so get the value from the model
        unique_filter[unique_field] = getattr(instance,unique_field)

    # try to find if any models already exist in the db;
    # I find all models and then exlude those matching the current model.
    existing_instances = type(instance).objects.filter(**unique_filter).exclude(pk=instance.pk)

    if existing_instances:
      # if we've gotten to this point, 
      # then there is a pre-existing model matching the unique filter
      # so record the relevant errors
      for unique_field in unique_fields:
        self.errors[unique_field] = "This value must be unique."

Answer 3

Model.Meta.unique_together 创建一个仅限于数据库的约束，而 ModelForm.is_valid() 主要基于正确的类型。如果它确实检查了约束，那么您将有一个竞争条件，仍然可能在 save() 调用中导致 IntegrityError。

您可能想要捕获 IntegrityError：

if new_accountadmin_form.is_valid():
    try:
        newaccountadmin_form.save()
    except IntegrityError, error:
        # here's your error handling code