django.db.utils.IntegrityError: NOT NULL contraint failed: appname_modelName.id

I am creating a client management system in django.

I have two models called 'Client' and 'Installment'. my 'models.py' file is given below:

models.py

from django.db import models
from django.utils import timezone
from django.urls import reverse
# Create your models here.


class Client(models.Model):
    name = models.CharField(max_length = 100)
    dob = models.SlugField(max_length = 100)
    CNIC = models.SlugField(max_length = 100)
    property_type = models.CharField(max_length = 100)
    down_payment = models.IntegerField()
    date_posted = models.DateTimeField(default=timezone.now)

    def __str__(self):
        return self.name


    def get_absolute_url(self):
        return reverse('client_details',kwargs={ 'pk' : self.pk})

class Installment(models.Model):
    client = models.ForeignKey(Client, blank=True, on_delete=models.CASCADE)
    installment_month = models.CharField(max_length = 100)
    installment_amount = models.IntegerField()
    installment_date = models.DateTimeField(default=timezone.now)

    def __str__(self):
        return self.installment_month

    def get_absolute_url(self):
        return reverse('installment_confirmation')

I am using ForeignKey in the installment model to link the Client model to it, because one client can have multiple installments.

When I RUN the following two commands

python manage.py makemigrations
python manage.py migrate

I didn't get any error.

Then I RUN the server using:

python manage.py runserver

and it runs successfully.

Then I add a new client in My app that uses client model.

But when I want to add installment to the client, is takes input from the user in the fields (installment_month and installment_month), and when I click 'add installment', it gives the following error:

IntegrityError at /1/Add-Installment
NOT NULL constraint failed: property_details_installment.client_id
Request Method: POST
Request URL:    http://127.0.0.1:8000/1/Add-Installment
Django Version: 2.1.3
Exception Type: IntegrityError
Exception Value:    
NOT NULL constraint failed: property_details_installment.client_id
Exception Location: /anaconda3/lib/python3.6/site-packages/django/db/backends/sqlite3/base.py in execute, line 296
Python Executable:  /anaconda3/bin/python3
Python Version: 3.6.5
Python Path:    
['/Users/razajaved/Documents/installment_plan',
 '/anaconda3/lib/python36.zip',
 '/anaconda3/lib/python3.6',
 '/anaconda3/lib/python3.6/lib-dynload',
 '/anaconda3/lib/python3.6/site-packages',
 '/anaconda3/lib/python3.6/site-packages/aeosa']
Server time:    Sun, 28 Mar 2021 13:55:36 +0000

What I tried next is that I removed the 'blank=True' parameter from the ForeignKey line in the installment model. and then it adds the installment successfully.

But, to check that the added installment is correctly corresponds to the added client. I went into the shell using the following command:

python manage.py shell

Once in the shell i did the following:

from property_details.models import Client
from property_details.models import Installment

Then I tried to check the client I added using the following command:

client1 = Client.objects.filter('clientName')

It works.

I can also check the added installment using the above command.

But when I RUN

client1.id

it gives the following error:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-4-abd51507c2e0> in <module>()
----> 1 client1.id

AttributeError: 'QuerySet' object has no attribute 'id'

But when I RUN

installment.id

it returns the id of the added installment.

It looks like, there is some problem with the ForeignKey I used in the installment model, and there is no id assigned to the client. I have tried different solution like putting 'blank=True' OR 'null=True' parameters. But it didn't work for me.

Does anyone has an idea how to solve this problem?