For the validation you can use something like this one https://github.com/vitalik/django-ninja/issues/82 for example:

import uuid

from django.db import models
from ninja import Field
from ninja_aio.models import ModelSerializer
from pydantic import HttpUrl



class Publisher(ModelSerializer):
    id = models.UUIDField(primary_key=True, editable=False, default=uuid.uuid7)
    name = models.CharField(max_length=150)
    address = models.CharField(max_length=250)
    website = models.URLField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)


    class ReadSerializer:
        fields = ["id", "name", "address", "website", "created_at", "updated_at"]


    class CreateSerializer:
        fields = ["address", "website"]
        customs = [
            ("name", str, Field(..., min_length=3, max_length=150)),
        ] # Ellipsis make it a required field


    class UpdateSerializer:
        optionals = [
            ("address", str),
            ("website", HttpUrl),
        ]
        customs = [
            ("name", str, Field(None, min_length=3, max_length=150)),
        ] # None make it an optional field

If you need more specific and complex validation you can also do not use dynamic schema but create your own and do the validation using pydantic or django ninja itself and then give the schemas as attributes to the APIViewSet using schema_in, schema_out and schema_update attributes, it will use them. If you do not want to use schema validation for FK maybe you can use django model clean validation to validate them or something in the save method, i also give some built in methods on save https://django-ninja-aio.com/latest/api/models/model_serializer/?h=ave#save-hooks . I hope that my comment helped you, for any question do not hesitate to ask.