null=True - Django Built-in Field Validation

null=True - Django Built-in Field Validation

In Django, when defining models, the null argument for a field specifies whether the database column backing the field should allow storing NULL values. In other words, it's a database-level constraint and dictates if the column can have a NULL value. This is different from the concept of a field being "required" at the form or serializer level.

Let's consider how null=True behaves for different field types:

  1. CharField and TextField

    If you use null=True on a CharField or TextField, Django documentation recommends also using blank=True. This is because an empty value on such fields will be saved as an empty string ("") in the database rather than as NULL.

    name = models.CharField(max_length=100, null=True, blank=True)

    Here, blank=True indicates that the field can be left blank in forms.

  2. ForeignKey

    When using null=True for a ForeignKey field, it means the relationship is optional. The referenced model is not a required association.

    author = models.ForeignKey(Author, on_delete=models.SET_NULL, null=True)

    In this case, if the referenced Author is deleted, the author field in the related model will be set to NULL.

  3. DateTimeField and DateField

    If you set null=True for a DateTimeField or DateField, it implies that this field can contain a NULL value in the database, which can be interpreted as the date/time being unknown.

    birthdate = models.DateField(null=True, blank=True)

  4. Other Fields

    For other fields like IntegerField, BooleanField, etc., using null=True means the database column can store NULL values.

    For BooleanField, there's a NullBooleanField if you need to represent three states: True, False, and NULL.

Note on Validation: The null argument only affects database storage (i.e., whether the DB column allows NULL values). It doesn't affect validation directly.

For form-level validation (e.g., when you're using a ModelForm), the blank argument is what dictates if a field is "required". If blank=False (the default), then the field is required in forms. If blank=True, the field is optional in forms.

Remember: Always consider the logical structure of your data and the requirements of your application when deciding whether to use null=True or blank=True or both.

More Tags

meteor vcf-vcard mozilla ibm-cloud stm32f0 pyuic attr stub ionicons margins

More Programming Guides

Other Guides

More Programming Examples