How to Implement this custom model manager in django?

Question

am new to Django and I getting some difficulties and I'm confused about the correct way to use Django custom model managers:

charities/models.py:

from django.db import models
from accounts.models import User

class Benefactor(models.Model):

    Level = ((0, 'Beginner'), (1, 'Intermediate'), (2, 'Expert'))

    user = models.OneToOneField(User, on_delete=models.CASCADE)
    experience = models.SmallIntegerField(choices=Level, default=0)
    free_time_per_week = models.PositiveSmallIntegerField(default=0)


class Charity(models.Model):

    user = models.OneToOneField(User, on_delete=models.CASCADE)
    name = models.CharField(max_length=50)
    reg_number = models.CharField(max_length=10)

class TaskManager(models.Manager):
    def related_tasks_to_charity(self, user):
        my_charity = str(Charity.objects.get(user = user))
        return self.filter(charity = my_charity)

    def related_tasks_to_benefactor(self, user):
        my_bonefactor = str(Benefactor.objects.get(user = user))
        return self.filter(assigned_benefactor = my_bonefactor)

    def all_related_tasks_to_user(self, user):
        return self.filter(state = "P")

class Task(models.Model):

    gen_choice = (('F', 'Female'), ('M', 'Male'))
    sta_choice = (('P', 'Pending'), ('W', 'Waiting'), ('A', 'Assigned'), ('D', 'Done '))

    # id = models.AutoField() !REMOVE id FIELDS 
    assigned_benefactor = models.ForeignKey(Benefactor, null=True, on_delete=models.SET_NULL)
    charity = models.ForeignKey(Charity, on_delete=models.CASCADE, related_name='User_Charity')
    age_limit_from = models.IntegerField(blank=True, null=True)
    age_limit_to = models.IntegerField(blank=True, null=True)
    date = models.DateField(blank=True, null=True)
    description = models.TextField(blank=True, null=True)
    gender_limit = models.CharField(max_length=50, blank=True, null=True)
    state = models.CharField(max_length=50, choices=sta_choice, default='Pending')
    title = models.CharField(max_length=100)
    objects = TaskManager()

my problem is here and these 3 defines:

class TaskManager(models.Manager):
        def related_tasks_to_charity(self, user):
            my_charity = str(Charity.objects.get(user = user))
            return self.filter(charity = my_charity)
    
        def related_tasks_to_benefactor(self, user):
            my_bonefactor = str(Benefactor.objects.get(user = user))
            return self.filter(assigned_benefactor = my_bonefactor)
    
        def all_related_tasks_to_user(self, user):
            return self.filter(state = "P")

def related_tasks_to_charity: In this function, return all the Tasks given to the user as charity in queryset format.

For example, if the user does not have a charity, obviously none of the Tasks are given to him as a charity, and your function must return the value none in a queryset.

def related_tasks_to_benefactor: In this function, return all the tasks given to the user as a benefactor in queryset format.

For example, if the user is not a benefactor, obviously none of the Tasks are given to him as a benefactor, and your function must return the value of none in the form of a queryset.

def all_related_tasks_to_user: In this function, return all the Tasks that the user has access to in a queryset format.

A user has access to Tasks whose status is Pending or given to the user as a benefactor or charity.

The function of this function is to return all these ‌Tasks as a queryset...

Answer 1

class TaskManager(models.Manager):
    def related_tasks_to_charity(self, user):
        return Task.objects.filter(charity__user=user)

    def related_tasks_to_benefactor(self, user):
        return Task.objects.filter(assigned_benefactor__user=user)

    def all_related_tasks_to_user(self, user):
        return Task.objects.filter(
            Q(state='P') | Q(charity__user=user) | Q(assigned_benefactor__user=user))