models.py

from django.db import models


class FuelType(models.Model):
    name = models.CharField(max_length=255)

    def __str__(self):
        return self.name


class CarModel(models.Model):
    name = models.CharField(max_length=255)
    fueltype = models.ManyToManyField(FuelType, related_name='models', through='ModelFuel')

    def __str__(self):
        return self.name


class ModelFuel(models.Model):
    fueltype = models.ForeignKey(FuelType, on_delete=models.CASCADE)
    carmodel = models.ForeignKey(CarModel, on_delete=models.CASCADE)
    name = models.CharField(max_length=255)

    def __str__(self):
        return self.name