How to Solve You are trying to add a non-nullable field to without a default

This problem occurs when attempting to add a field to a model in your database schema that doesn't allow null values, but you haven't provided a default value for existing records.

Let's say I have this model below:

class test(models.Model):
    p_1 = models.CharField(max_length=300)
    p_2 = models.CharField(max_length=300)
    p_3 = models.CharField(max_length=300)
    def __str__(self):
        return(self.p_1)

And I need to add another field to my test model,

class test(models.Model):
    p_1 = models.CharField(max_length=300)
    p_2 = models.CharField(max_length=300)
    p_3 = models.CharField(max_length=300)
    p_4 = models.CharField(max_length=300) #new field
    def __str__(self):
        return(self.p_1)

If I migrate my models, I will get the issue:

You are trying to add a non-nullable field 'p_4' to header_slider without a default; we can't do that (the database needs something to populate existing rows).

So, how to solve this issue?

1. Adding 'null = True' parametre.

In Django, the null parameter is used in model fields to specify whether a field can be set as NULL in the database. We must add the parameter to our new field to solve the issue.

Code:

p_4 = models.CharField(max_length=300, null=True) #new field

Now we can migrate the models, and the issue will be solved.

2. Adding 'default = " " ' parameter

In Django models, the default parameter specifies a field's default value when no explicit value is provided. Here is how to set it:

p_6 = models.CharField(max_length=300, default='test') # default value

If neither of these two methods proves effective, you can attempt the following solution:

3. Deleting and returning the model

Before discussing this solution, I emphasize that this way will delete your model data.

Here are the steps:

1. Delete the model class from models.py

2. Run the migrations:

3. Add back the model class in models.py

4. Run the migrations again