How tortoise implements the same functionality as SerializerMethodField in DRF?

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from rest_framework import serializers
from drf_spectacular.utils import extend_schema_field


class UserSerializer(serializers.ModelSerializer):
    full_name = serializers.SerializerMethodField(read_only=True)
    
    @extend_schema_field(serializers.CharField)
    def full_name(self, obj):
        return f'{obj.first_name}:{obj.id}'

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The issue names no repository files, tests, or entry points. Start by locating Tortoise's serializer-related integration and compare it with the shown DRF SerializerMethodField example; clarify the intended API and define the expected behavior before implementation.