django - 如何与 prefetch 相关和 prefetch 进行聚合

Question

我有两个模型诊所和 ClinicCredits:我想要一份带有可用余额的诊所列表问题是，如果我使用注释，我必须使用 ClinicCredits 的查询集循环获取可用的平衡:

class Clinic(models.Model):
    """
    clinic model
    """
    user = models.OneToOneField(User, related_name="clinic", primary_key=True, 
     on_delete=models.CASCADE)

    def __str__(self):
        return self.name

    class Meta:
        db_table = 'clinic'




 class ClinicCredits(models.Model):
 """
  credit details for clinic
 """
    clinic = models.ForeignKey(Clinic, on_delete=models.CASCADE, related_name='c_credits')
    credits = models.FloatField('credits', default=0.0)
    balance = models.FloatField('balance', default=0.0, help_text="balance after deduction of credits")

    def __str__(self):
        return self.clinic.name

    class Meta:
       db_table = 'clinic_credits'

这是我获取诊所的查询:

    clinics = Clinic.objects.filter(practice_id__in=user.dietitian.practiceid).order_by(
        'user__date_joined').prefetch_related(Prefetch('c_credits',ClinicCredits.objects.filter(balance__gt=0),'credit_'))

在这种情况下我如何使用聚合，或者是否有其他方法来检索诊所列表及其可用信用。

Answer 1

您可以使用annotate(...)这样尝试:

clinics = Clinic.objects.filter(
    practice_id__in=user.dietitian.practiceid
).order_by('user__date_joined').prefetch_related(
    Prefetch(
        'c_credits',
        ClinicCredits.objects.filter(balance__gt=0),
        'credit_'
    )
)<b>.annotate(
    total_cred=Sum('c_credits__balance')
)</b>