Python 使用Django为多个反向外键选择相关和预取相关？

我当前在访问queryset中的值时遇到问题。我的应用程序有一个models.py，设置如下：

class Company(models.Model):
    name = models.Charfield(max_length=250)

class Patient(models.Model):

        status_choices = [
        ('A', 'Current Admission'),
        ('D', 'Discharged'),
        ('U', 'Unknown'),
    ]

    first_name = models.CharField(max_length=250)
    last_name = models.CharField(max_length=250)
    patient_status = models.CharField(
        max_length=15,
        choices=status_choices,
        null=True, default='U',
        verbose_name='Patient Status'
    )
    related_company = models.ForeignKey(Company, on_delete=models.CASCADE, related_name='patients')

class PatientStay(models.Model):
    admit_date = models.DateField()
    projected_dc_date = models.DateField(null=True, blank=True)
    is_active = models.BooleanField(default=False)
    stay_to_patient_relationship = models.ForeignKey(Patient, on_delete=models.CASCADE, related_name='stays')
    
class PatientLOC(models.Model):
    loc_to_stay_relation = models.ForeignKey(PatientStay, on_delete=models.CASCADE, related_name='locs')
    level_of_care = models.CharField(max_length=30)
    loc_start = models.DateField(null=True)
    loc_end = models.DateField(null=True, blank=True)
    is_active = models.BooleanField(default=False)

company = Company.objects.select_related().prefetch_related('patients__stays', 'patients__stays__locs').get(id=2)

patients = company.patients.all()

for patient in patients:
    ...:     print(patient)
    ...:     print(patient.stays.all())

我试图做的是查询（对于特定公司）患者、他们的相关住院时间（仅针对活跃期进行筛选）以及他们的相关PatientLOC

这样的结果：

class Company(models.Model):
    name = models.Charfield(max_length=250)

class Patient(models.Model):

        status_choices = [
        ('A', 'Current Admission'),
        ('D', 'Discharged'),
        ('U', 'Unknown'),
    ]

    first_name = models.CharField(max_length=250)
    last_name = models.CharField(max_length=250)
    patient_status = models.CharField(
        max_length=15,
        choices=status_choices,
        null=True, default='U',
        verbose_name='Patient Status'
    )
    related_company = models.ForeignKey(Company, on_delete=models.CASCADE, related_name='patients')

class PatientStay(models.Model):
    admit_date = models.DateField()
    projected_dc_date = models.DateField(null=True, blank=True)
    is_active = models.BooleanField(default=False)
    stay_to_patient_relationship = models.ForeignKey(Patient, on_delete=models.CASCADE, related_name='stays')
    
class PatientLOC(models.Model):
    loc_to_stay_relation = models.ForeignKey(PatientStay, on_delete=models.CASCADE, related_name='locs')
    level_of_care = models.CharField(max_length=30)
    loc_start = models.DateField(null=True)
    loc_end = models.DateField(null=True, blank=True)
    is_active = models.BooleanField(default=False)

company = Company.objects.select_related().prefetch_related('patients__stays', 'patients__stays__locs').get(id=2)

patients = company.patients.all()

for patient in patients:
    ...:     print(patient)
    ...:     print(patient.stays.all())

• 公司：
• -病人
• --停留
• ---LOC's
• -病人
• --停留
• ---LOC's
• -病人
• --停留
• ---LOC's

我提出了以下建议（过滤除外）：

我可以通过这个循环找到病人和住院病人，但我似乎无法找到那些病人的LOC。所以，我可以这样做：

class Company(models.Model):
    name = models.Charfield(max_length=250)

class Patient(models.Model):

        status_choices = [
        ('A', 'Current Admission'),
        ('D', 'Discharged'),
        ('U', 'Unknown'),
    ]

    first_name = models.CharField(max_length=250)
    last_name = models.CharField(max_length=250)
    patient_status = models.CharField(
        max_length=15,
        choices=status_choices,
        null=True, default='U',
        verbose_name='Patient Status'
    )
    related_company = models.ForeignKey(Company, on_delete=models.CASCADE, related_name='patients')

class PatientStay(models.Model):
    admit_date = models.DateField()
    projected_dc_date = models.DateField(null=True, blank=True)
    is_active = models.BooleanField(default=False)
    stay_to_patient_relationship = models.ForeignKey(Patient, on_delete=models.CASCADE, related_name='stays')
    
class PatientLOC(models.Model):
    loc_to_stay_relation = models.ForeignKey(PatientStay, on_delete=models.CASCADE, related_name='locs')
    level_of_care = models.CharField(max_length=30)
    loc_start = models.DateField(null=True)
    loc_end = models.DateField(null=True, blank=True)
    is_active = models.BooleanField(default=False)

company = Company.objects.select_related().prefetch_related('patients__stays', 'patients__stays__locs').get(id=2)

patients = company.patients.all()

for patient in patients:
    ...:     print(patient)
    ...:     print(patient.stays.all())

但这样的事情是行不通的：

company = Company.objects.select_related().prefetch_related('patients__stays', 'patients__stays__locs').get(id=2)
patients = company.patients.all()

for patient in patients:
     ...:     print(patient)
     ...:     for stay in patient.stays.all():
     ...:         print(stay)
     ...:         for loc in patient.stays.locs.all():
     ...:             print(loc)

除了我使用一堆嵌套for循环之外，最好的方法是什么？在psuedocode中，有没有一种方法可以像这样对患者进行循环：

for patient in patients:
    print(patient)
    print(patient.stay)
    print(patient.stay.loc)

我已经为此挣扎了一段时间，我已经猜不出来了。文档让我找到了与select_相关的和prefetch_相关的（我确信我在某种程度上使用了错误的方法）

---

感谢您的帮助。

您可以嵌套预回迁电话：

from django.db.models import Prefetch
patients = Patient.objects.filter(company__id=2).prefetch_related(
   Prefetch(
      'stays',
      queryset=PatientStay.objects.prefetch_related('locs')
   ))

for patient in patients:
   print(patient)
   print([stay for stay in patient.stays.all()])
   print([loc for stay in patient.stays.all() for loc in stay.locs.all()])

---

仅供参考：

select\u related

在这里没有为您做任何事情。与预取相关的操作只会保存数据库行程。如果您不关心查询，那么嵌套for循环代码的唯一问题是patient.stays.locs.all（）的行

-这将是loc in staid.locs.all（）的
-您就快到了！这非常有用，感谢您提供嵌套的预回迁呼叫信息。如何从模板访问此文件？我不能（至少我可以看到）在模板中使用列表理解，也不会像stay-in-patient.stay.filter（is_-active=True）那样使用任何内容。我是否需要以某种方式在我的视图函数中执行这些操作，然后以这种方式保存它们>作为上下文传递？我正在为这一个而奋斗。没关系，我能够循环通过它，但我必须在没有理解的情况下使用Django过滤器，而不是queryset过滤器。