Django在多对二多中间表中创建了一个额外的不需要的条目

from django.db import models

class ModelA(models.Model):
    name = models.CharField(max_length=100)
    models_b = models.ManyToManyField('ModelB', through='ModelAB')

class ModelB(models.Model):
    name = models.CharField(max_length=100)

class ModelAB(models.Model):
    model_a = models.ForeignKey(ModelA, on_delete=models.CASCADE)
    model_b = models.ForeignKey(ModelB, on_delete=models.CASCADE)
    extra_field = models.CharField(max_length=100)