Issue

Here is my code:

Importing models from django.db


Class parent (models.Model):
    Name = models.CharField(max_length=50, unique=True)

    def __str__(self):
        return str(self.name)


Children of the class (models.Model):
    Parent = models.ForeignKey(Parent, on_delete=models.CASCADE)
    Name = models.CharField(max_length=50, unique=True)
    
    def __str__(self):
        return str(self.name)
 

Parent in database:

Logan

Smith

Dough

Management Dashboard:

First I created a child named John and his parent is he Smith.. worked!

After that, every time you create a child named John, this time with a parent of Doe or Rogan, you will see:

“A child with this name already exists.”

I’ve searched on Google but can’t seem to find an answer.

Solution

You work with a UniqueConstraint ^[Django-doc]:

class Child(models.Model):
    parent = models.ForeignKey(Parent, on_delete=models.CASCADE)
    name = models.CharField(max_length=50)

    def __str__(self):
        return f'{self.name}'

    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=('name', 'parent_id'), name='unique_child_name_per_parent'
            )
        ]

Answered By – Willem Van Onsem

Answer Checked By – Pedro (Easybugfix Volunteer)

Tags: database, django, model, python, unique-constraint