unique=True – Django Built-in Field Validation

Built-in Field Validations in Django models are the validations that come predefined to all Django fields. Every field comes in with built-in validations from Django validators. One can also add more built-in field validations for applying or removing certain constraints on a particular field. unique=True sets the field to be unique i.e. once entered a value in a field, the same value can not be entered in any other instance of that model in any manner. It is generally used for fields like Roll Number, Employee Id, etc which should be unique. 

Syntax:

field_name = models.Field(unique=True)

Django Built-in Field Validation unique=True Explanation

Illustration of unique using an Example. Consider a project named geeksforgeeks having an app named geeks.

Refer to the following articles to check how to create a project and an app in Django.

• How to Create a Basic Project using MVT in Django?
• How to Create an App in Django ?

Enter the following code into models.py file of geeks app. We will be using CharField for experimenting for all field options. 

After running makemigrations and migrate on Django and rendering the above model, let us create an instance from Django admin interface with string “a“. Now to show the constraint of unique=True, let us try to create one more instance of the model using same string. Now it will show this error.

Advanced concepts with unique

This is enforced at the database level and by model validation. If you try to save a model with a duplicate value in a unique field, a django.db.IntegrityError will be raised by the model’s save() method. This option is valid on all field types except ManyToManyField and OneToOneField. Note that when unique is True, you don’t need to specify db_index, because unique implies the creation of an index.

More Built-in Field Validations