Question

我有一些模特以父母-孩子-孩子的孩子的方式。在我的views.py中，我做到了 swsallsteps = sws_dcoument_step.objects.filter().prefetch_related(my various models)

我遇到的问题是如何从相关信息中预取相关信息？我在这部分迷路了。示例我的views.py

  swsallsteps = SWS_Document_Step.objects\
      .filter(document_number=document_id)\
      .prefetch_related('swes_step_set', 'sws_step_hazard_set', 'sws_step_ppe_set')

这恰好返回了我的期望。与SWS_Document_Step关联的SWES_Step_Set类似于下面的前两个模型。但是，如何拉出与SWES_Document_Step关联的SWES_Step_Picture模型？我想这比我做的要简单得多。

以下示例为模型。

class SWS_Document_Step(models.Model):

    STEP_TYPE_CHOICES = (
        ('People', 'People'),
        ('Quality', 'Quality'),
        ('Velocity', 'Velocity'),
        ('Cost', 'Cost'),
    )
    document_number = models.ForeignKey(SWS_Document, on_delete=models.CASCADE)
    sws_sequence_number = models.PositiveIntegerField(editable=True, null=True)
    sws_work_element_description = models.CharField(max_length=500)
    sws_step_type = models.CharField(max_length=30, choices=STEP_TYPE_CHOICES, null=True, blank=True)
    pub_date = models.DateTimeField(auto_now=True)

    class Meta:
        verbose_name = 'SWS Document Step'
        verbose_name_plural = '005 SWS Document Steps'

    def __str__(self):
        return str(self.document_number) + " " + str(self.sws_sequence_number) + " " + str(self.sws_work_element_description)

class SWES_Step(models.Model):

    STEP_TYPE_CHOICES = (
        ('People', 'People'),
        ('Quality', 'Quality'),
        ('Velocity', 'Velocity'),
        ('Cost', 'Cost'),
    )
    sws_document_id = models.ForeignKey(SWS_Document_Step, on_delete=models.CASCADE, null=True)
    swes_description = models.CharField(max_length=500)
    swes_step_type = models.CharField(max_length=8, choices=STEP_TYPE_CHOICES, blank=True)
    pub_date = models.DateTimeField(auto_now=True)

    class Meta:
        verbose_name = 'SWES Step'
        verbose_name_plural = '012 SWES Document Steps'

    def __str__(self):
        return str(self.sws_document_id) + " " + str(self.swes_description)

class SWES_Step_Picture(models.Model):

    swes_step = models.ForeignKey(SWES_Step, on_delete=models.CASCADE)
    sws_step_photo = models.ImageField()
    pub_date = models.DateTimeField(auto_now=True)

    class Meta:
        verbose_name = 'SWES Step Picture'
        verbose_name_plural = '015 SWES Step Pictures'

Answer 1

IDentityUser

抱歉，不禁重命名了您的模型，它们只是不执行操作的示例：

1。Don't使用>>> from django_single.models import * >>> SWSDocumentStep.objects.select_related('document_number').prefetch_related('swesstep_set', 'swesstep_set__swessteppicture_set') DEBUG (0.004) SELECT "django_single_swsdocumentstep"."id", "django_single_swsdocumentstep"."document_number_id", "django_single_swsdocumentstep"."sws_sequence_number", "django_single_swsdocumentstep"."sws_work_element_description", "django_single_swsdocumentstep"."sws_step_type", "django_single_swsdocumentstep"."pub_date", "django_single_swsdocument"."id", "django_single_swsdocument"."name" FROM "django_single_swsdocumentstep" INNER JOIN "django_single_swsdocument" ON ("django_single_swsdocumentstep"."document_number_id" = "django_single_swsdocument"."id") WHERE "django_single_swsdocumentstep"."id" = 10 LIMIT 21; args=(10,) DEBUG (0.001) SELECT "django_single_swesstep"."id", "django_single_swesstep"."sws_document_id", "django_single_swesstep"."swes_description", "django_single_swesstep"."swes_step_type", "django_single_swesstep"."pub_date" FROM "django_single_swesstep" WHERE "django_single_swesstep"."sws_document_id" IN (10); args=(10,) DEBUG (0.002) SELECT "django_single_swessteppicture"."id", "django_single_swessteppicture"."swes_step_id", "django_single_swessteppicture"."pub_date" FROM "django_single_swessteppicture" WHERE "django_single_swessteppicture"."swes_step_id" IN (10); args=(10,) <QuerySet [<SWSDocumentStep: SWSDocument object (10) None >]>并将ForeignKey添加到模型的末尾，例如：_id> sws_document_id

2。在python中，我们不会在类中的单词之间添加sws_document，例如：_> SWES_Step_Picture

SWESStepPicture

# to get this to work you will need to do the following steps
mkdir django_simple/migrations
touch django_simple/django_simple.py
# copy and paste the content of the file bellow in django_simple/django_simple.py
python django_simple/django_simple.py makemigrations
python django_simple/django_simple.py migrate
python django_simple/django_simple.py shell -c 'from django_simple.models import *; SWESStepPicture.objects.create(swes_step=SWESStep.objects.create(sws_document=SWSDocumentStep.objects.create(document_number=SWSDocument.objects.create(name="blah"))))'

Django prefetch相关的prefetched相关

1 个答案: