后续行动：在Django Modelform中缺少必需的Charfield被保存为空字符串，并且不会引发错误

Question

If I try to save incomplete model instance in Django 1.10, I would expect Django to raise an error. It does not seem to be the case.

models.py:

from django.db import models

class Essai(models.Model):
    ch1 = models.CharField(max_length=100, blank=False)
    ch2 = models.CharField(max_length=100, blank=False)

So I have two fields not allowed to be empty (default behavior, NOT NULL restriction is applied by Django at MySQL table creation). I expect Django to rase an error if one of the fields is not set before storing.

However, when I create an incomplete instance, the data is stored just fine:

>>> from test.models import Essai
>>> bouh = Essai()
>>> bouh.ch1 = "some content for ch1"
>>> bouh.save()
>>> bouh.id
9
>>> bouh.ch1
'some content for ch1'
>>> bouh.ch2
''
>>> 

I would have expected Django to raise an error. If I force ch2 to None , however, it raises an error:

>>> bouh = Essai()
>>> bouh.ch1 = "some content for ch1"
>>> bouh.ch2 = None
>>> bouh.save()
Traceback (most recent call last):
  (...)
    return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: NOT NULL constraint failed: test_essai.ch2
>>> bouh.id
>>> bouh.ch1
'some content for ch1'
>>> bouh.ch2
>>>

Explanation: Django is not raising an error as default behavior in this simple case because in SQL empty string "" is not equivalent to NULL, as stated in Django model blank=False does not work?

Now, if we look at ModelForm behavior, there seem to be a inconsistency in django doc:

According to: https://docs.djangoproject.com/en/1.10/topics/forms/modelforms/#selecting-the-fields-to-use

Django will prevent any attempt to save an incomplete model, so if the model does not allow the missing fields to be empty, and does not provide a default value for the missing fields, any attempt to save() a ModelForm with missing fields will fail. To avoid this failure, you must instantiate your model with initial values for the missing, but required fields:(…)

a modelForm should not be saved with a missing field if there is no default value.

So with this ModelForm: class EssaiModelForm(forms.ModelForm): class Meta: model = Essai fields = ['ch1'] A form with only one field ch1 is generated.

• If ch1 is left empty, the validation fails at EssaiModelFormInstance.is_valid() as expected.
• If ch1 contains a value, the validation succeeds even though ch2 is still missing. Then the EssaiModelFormInstance.save() succeeds, contrary to what is claimed in django documentation. ch2 is empty string and thus is compatible with SQL requirements ( NOT NULL ).

So it seems that there is a default default value empty string "" for Charfield that is not accepted in form validation but that is accepted in save() validation. This may require clarification in the documentation.

Answer 1

As the two fields ch1 and ch2 are always required in your case, all you need to do is modify your model such that

from django.db import models

class Essai(models.Model):
    ch1 = models.CharField(max_length=100)
    ch2 = models.CharField(max_length=100)

and include the fields in the form as

class EssaiModelForm(forms.ModelForm):
class Meta:
    model = Essai
    fields = ['ch1', 'ch2']

Django will automatically raise a validation error for this fields on is_valid()

Or if you want to disallow empty string inputs to these fields blank=False will not work

Refer this Django - how to set blank = False, required = False

Answer 2

There is a slightly notable difference in model and it's forms. Model.save() performs no validation. So if it fails then probably it raises a database level IntegrityError. For reducing risks of failure at database layer one need to call Model.full_clean() which is also done by ModelForm as documented here in django's validating objects .

In my opinion, I expect from django that ModelForms are meant to validate and save data entered by client. Model instantiated programmatically should follow the same control before saving into database.