giving models a custom manager you can use a custom manager in a particular model by extending the base manager class and instantiating your custom manager in your model there are two reasons you might want to customize a manager to add extra manager methods andor to modify the initial queryset the manager returns queryset with an init method that takes an additional argument queryset with an __init__ method that takes an additional argument
from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation
from django.db import models


class PersonManager(models.Manager):
    def get_fun_people(self):
        return self.filter(fun=True)


class PublishedBookManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(is_published=True)


class AnnotatedBookManager(models.Manager):
    def get_queryset(self):
        return (
            super()
            .get_queryset()
            .annotate(favorite_avg=models.Avg("favorite_books__favorite_thing_id"))
        )


class CustomQuerySet(models.QuerySet):
    def filter(self, *args, **kwargs):
        queryset = super().filter(fun=True)
        queryset._filter_CustomQuerySet = True
        return queryset

    def public_method(self, *args, **kwargs):
        return self.all()

    def _private_method(self, *args, **kwargs):
        return self.all()

    def optout_public_method(self, *args, **kwargs):
        return self.all()

    optout_public_method.queryset_only = True

    def _optin_private_method(self, *args, **kwargs):
        return self.all()

    _optin_private_method.queryset_only = False


class BaseCustomManager(models.Manager):
    def __init__(self, arg):
        super().__init__()
        self.init_arg = arg

    def filter(self, *args, **kwargs):
        queryset = super().filter(fun=True)
        queryset._filter_CustomManager = True
        return queryset

    def manager_only(self):
        return self.all()


CustomManager = BaseCustomManager.from_queryset(CustomQuerySet)


class CustomInitQuerySet(models.QuerySet):
    
    def __init__(
        self, custom_optional_arg=None, model=None, query=None, using=None, hints=None
    ):
        super().__init__(model=model, query=query, using=using, hints=hints)


class DeconstructibleCustomManager(BaseCustomManager.from_queryset(CustomQuerySet)):
    def __init__(self, a, b, c=1, d=2):
        super().__init__(a)


class FunPeopleManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(fun=True)


class BoringPeopleManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(fun=False)


class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    fun = models.BooleanField(default=False)

    favorite_book = models.ForeignKey(
        "Book", models.SET_NULL, null=True, related_name="favorite_books"
    )
    favorite_thing_type = models.ForeignKey(
        "contenttypes.ContentType", models.SET_NULL, null=True
    )
    favorite_thing_id = models.IntegerField(null=True)
    favorite_thing = GenericForeignKey("favorite_thing_type", "favorite_thing_id")

    objects = PersonManager()
    fun_people = FunPeopleManager()
    boring_people = BoringPeopleManager()

    custom_queryset_default_manager = CustomQuerySet.as_manager()
    custom_queryset_custom_manager = CustomManager("hello")
    custom_init_queryset_manager = CustomInitQuerySet.as_manager()

    def __str__(self):
        return "%s %s" % (self.first_name, self.last_name)


class FunPerson(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    fun = models.BooleanField(default=True)
    favorite_book = models.ForeignKey(
        "Book",
        models.SET_NULL,
        null=True,
        related_name="fun_people_favorite_books",
    )
    favorite_thing_type = models.ForeignKey(
        "contenttypes.ContentType", models.SET_NULL, null=True
    )
    favorite_thing_id = models.IntegerField(null=True)
    favorite_thing = GenericForeignKey("favorite_thing_type", "favorite_thing_id")

    objects = FunPeopleManager()


class Book(models.Model):
    title = models.CharField(max_length=50)
    author = models.CharField(max_length=30)
    is_published = models.BooleanField(default=False)
    authors = models.ManyToManyField(Person, related_name="books")
    fun_authors = models.ManyToManyField(FunPerson, related_name="books")
    favorite_things = GenericRelation(
        Person,
        content_type_field="favorite_thing_type",
        object_id_field="favorite_thing_id",
    )
    fun_people_favorite_things = GenericRelation(
        FunPerson,
        content_type_field="favorite_thing_type",
        object_id_field="favorite_thing_id",
    )

    published_objects = PublishedBookManager()
    annotated_objects = AnnotatedBookManager()

    class Meta:
        base_manager_name = "annotated_objects"


class FastCarManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(top_speed__gt=150)


class Car(models.Model):
    name = models.CharField(max_length=10)
    mileage = models.IntegerField()
    top_speed = models.IntegerField(help_text="In miles per hour.")
    cars = models.Manager()
    fast_cars = FastCarManager()


class FastCarAsBase(Car):
    class Meta:
        proxy = True
        base_manager_name = "fast_cars"


class FastCarAsDefault(Car):
    class Meta:
        proxy = True
        default_manager_name = "fast_cars"


class RestrictedManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(is_public=True)


class RelatedModel(models.Model):
    name = models.CharField(max_length=50)


class RestrictedModel(models.Model):
    name = models.CharField(max_length=50)
    is_public = models.BooleanField(default=False)
    related = models.ForeignKey(RelatedModel, models.CASCADE)

    objects = RestrictedManager()
    plain_manager = models.Manager()


class OneToOneRestrictedModel(models.Model):
    name = models.CharField(max_length=50)
    is_public = models.BooleanField(default=False)
    related = models.OneToOneField(RelatedModel, models.CASCADE)

    objects = RestrictedManager()
    plain_manager = models.Manager()


class AbstractPerson(models.Model):
    abstract_persons = models.Manager()
    objects = models.CharField(max_length=30)

    class Meta:
        abstract = True


class PersonFromAbstract(AbstractPerson):
    pass