AbstractBaseUser.get_username() missing 1 required positional argument: 'self' | Error while accessing current user's username - django-models

Question

I am trying to access the Id of current logged in User. but i am getting the below error.
models.py of derived model
from django.db import models
from django.urls import reverse, reverse_lazy
from django.utils import timezone
from accounts.models import CustomUser
# Create your models here.
class PostProblem(models.Model):
problem_type_choices = (
('c','Confidential'),
('sc','Semi-confidential'),
('p','Public')
)
problem_category_choices = (
('agriculture','Agriculture'),
('computer_science','Computer Science'),
('social_studies','Social Studies'),
('environment','Environmental Science'),
('mathematics','Mathematics'),
('engineering','Engineering'),
('physics','physics'),
('chemistry','chemistry'),
('other','Other')
)
author = models.ForeignKey("accounts.CustomUser", verbose_name= "Creater", default = CustomUser.get_username ,on_delete=models.CASCADE)
problem_title = models.CharField(max_length=200, verbose_name="Problem's title")
problem_type = models.CharField(choices=problem_type_choices,max_length=5, verbose_name='Confidentiality of the problem ')
problem_category = models.CharField(choices=problem_category_choices, max_length=50, verbose_name="Catrgory of the problem")
problem_brief = models.CharField(max_length=1000, verbose_name='Breif description of the problem ')
problem_description = models.TextField(verbose_name='Problem complete description ')
problem_reward = models.IntegerField(verbose_name='Prize money for providing the solution ')
created_date = models.DateTimeField(default=timezone.now)
published_date = models.DateTimeField(blank=True, null=True)
def publish(self):
self.published_date = timezone.now
self.save()
def __str__(self):
return self.problem_title
def get_absolute_url(self):
return reverse("problem_detail", kwargs={"pk": self.pk})
def approve_solutions(self):
return self.solutions.filter(approved_solutions = True)
views.py
from django.shortcuts import render
from django.urls import reverse_lazy
from django.utils import timezone
from django.contrib.auth.mixins import LoginRequiredMixin
from problems.models import PostProblem, Solutions
from problems.forms import PostProblemForm, SolutionsForm
from django.views.generic import TemplateView, CreateView, DetailView, DeleteView, UpdateView, ListView
# Create your views here.
class PostProblemCreateView(CreateView, LoginRequiredMixin):
login_url = 'login/'
redirect_field_name = 'problems/problem_detail.html'
form_class = PostProblemForm
model = PostProblem
forms.py
from django import forms
from problems.models import PostProblem, Solutions
class PostProblemForm(forms.ModelForm):
class Meta:
model = PostProblem
fields = ("problem_title","problem_type","problem_category","problem_brief","problem_description","problem_reward")
widgets = {
'problem_title':forms.TextInput(attrs={'class':'textinputclass'}),
'problem_type': forms.TextInput(attrs={'class':'choice_input'}),
'problem_category':forms.TextInput(attrs={'class':'choice_input'}),
'problem_brief': forms.Textarea(attrs={'class':'editable medium-editor-textarea post_brief'}),
'problem_description': forms.Textarea(attrs={'class':'editable medium-editor-textarea post_complete'}),
'problem_reward': forms.TextInput(attrs={'class':'textinputclass'})
}
model.py of base model
from django.db import models
from django.contrib import auth
from django.urls import reverse
# Create your models here.
# for custom user
from django.contrib.auth.models import AbstractBaseUser, PermissionsMixin, User
from .managers import CustomUserManager
class CustomUser(AbstractBaseUser, PermissionsMixin):
'''Model representation for user'''
user_type_choices = (
('ps','Problem Solver'),
('pp','Problem Provider')
)
account_type_choices = (
('o','Organization'),
('i','Individual')
)
user_type = models.CharField(max_length=5, choices=user_type_choices, default='pp', verbose_name="Who you are? ")
account_type = models.CharField(max_length=5, choices= account_type_choices, default='o', verbose_name="Account Type ")
email = models.EmailField(max_length=50, unique=True, blank=False, verbose_name="Your Email ")
is_active = models.BooleanField(default=True) # anyone who signs up for thsi application is by default an active user
is_admin = models.BooleanField(default=False)
is_staff = models.BooleanField(default=False)
is_superuser = models.BooleanField(default=False) # the person who has highest level of control over database
# need to specify manager class for this user
objects = CustomUserManager()
# we are not placing password field here because the password field will always be required
REQUIRED_FIELDS = ['user_type', 'account_type']
USERNAME_FIELD = 'email'
EMAIL_FIELD = 'email'
I searched the web for answers but they have mentioned only about accessing current user id in function based views. How can I resolve this kind of error? I am new to Django.