Helper classes and a monkeypatch to always register a model's field in the admin as raw_id_fields. This is useful when you have models with 1000+ rows to avoid massive select elements.

admin_meta.py

from functools import wraps

from django.contrib import admin



class AdminMeta:
    """
    Use this Meta class on a model since we can't add
    custom fields to Model.Meta
    """
    always_raw_id_field = False

def patch_model_admin_always_raw_id_field():
    """
    Monkey patch admin.ModelAdmin to dynamically register
    additional raw_id_fields.

    This is best used in an AppConfig.ready() method
    """
    def patch_model_admin(init):
        @wraps(init)
        def __init__(self, model, admin_site, **kwargs):
            init(self, model, admin_site, **kwargs)
            # iterate over relationship fields, check if any related models are AdminMeta.always_raw_id_field
            new_raw_ids_fields = [
                field.name
                for field in model._meta.get_fields()
                if field.is_relation
                and field.related_model
                and field.concrete
                and (admin_meta := getattr(field.related_model, AdminMeta.__name__, None))
                and issubclass(admin_meta, AdminMeta)
                and admin_meta.always_raw_id_field
            ]
            if new_raw_ids_fields:
                self.raw_id_fields = list(self.raw_id_fields) + new_raw_ids_fields
        return __init__

    if getattr(admin.ModelAdmin, '_patched_model_admin_always_raw_id_field', None):
        return
    admin.ModelAdmin.__init__ = patch_model_admin(admin.ModelAdmin.__init__)
    admin.ModelAdmin._patched_model_admin_always_raw_id_field = True

always_raw_id.py

from django.db import models
from admin_meta import AdminMeta


class AlwaysRawIdModel(models.Model):
    """
    Inherit from this model so that any reference to this
    field in the admin will be a raw id field
    """
    class Meta:
        abstract = True

    class AdminMeta(AdminMeta):
        always_raw_id_field = True

my_apps.py

from django.apps import AppConfig

from admin_meta import patch_model_admin_always_raw_id_field


class MyApp(AppConfig):
    name = "my_app"

    def ready(self):
        patch_model_admin_always_raw_id_field()

my_models.py

from django.contrib.admin
from always_raw_id import AlwaysRawIdModel


class MyModel(AlwaysRawIdModel):
    pass

class OtherModel(models.Model):
    class AdminMeta(AdminMeta):
        always_raw_id_field = True


admin.register(MyModel)
admin.register(OtherModel)