[Django]-Django: How do I validate unique_together from within the model

by

8👍

✅

There are two options:

a) Have a try block where you save your model and capture the IntegrityError and deal with it. Something like:

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) In the clean() method of your form, check if the a row exists and raise a forms.ValidationError with an appropriate message. Example here.

So, b) it is… That is why I referenced the documentation; all you need is there.

But it would be something like:

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

For what it is worth – I just realized that your unique_together above is referencing a field called username that is not represented in the model.

The clean method above is called after all clean methods for the individual fields are called.

👤cethegeek

2👍

And for a completely generic way. In the model have the following two 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

and

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

And in the form have the following 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."
👤trubliphone

1👍

Model.Meta.unique_together creates a constraint limited to the database, while ModelForm.is_valid() is primarily based on correct types. Event if it did check constraints you would have a race condition that could still cause an IntegrityError in the save() call.

You probably want to be catching IntegrityError:

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

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