有外键时，django-import-export速度较慢

Question

当模型中有外键时，导出非常慢，当我排除外键没有问题时，它开始快速下载。这里的问题可能是什么？谢谢!

我的代码是这样的

resources.py

class InvoiceResource(resources.ModelResource):
  class Meta:
      model = Invoices

views.py

def export_invoice(request):
  person_resource = InvoiceResource()
  dataset = person_resource.export()
  response = HttpResponse(dataset.xlsx, content_type='application/vnd.ms-excel')
  response['Content-Disposition'] = 'attachment; filename="invoices.xlsx"'
  return response

models.py

class Invoices(models.Model):
   store_code = models.ForeignKey(MasterData, on_delete=models.CASCADE, db_column='Store Code', blank=True, null=True, verbose_name='Store Code')
   erp_id = models.CharField(db_column='ERP ID', max_length=200, blank=True, null=True, verbose_name='ERP ID')
   store_name = models.CharField(db_column='Store Name', max_length=200, blank=True, null=True, verbose_name='Store Name')

Answer 1

我认为你应该使用select_related

class ModelA(models.Model):
    fk = models.Foreingkey(ModelB)

class ModelB(models.Model):
    title = models.CharField(max_lenght=20)

如果您使用：

a_objects = ModelA.objects.all()

for obj in a_objects:
    fk = obj.fk

每个对象都需要对数据库进行查询

但是如果你使用

a_objects = ModelA.objects.all().select_related('fk')

for obj in a_objects:
    fk = obj.fk

在这种情况下，只有一次对数据库的查询。

有关更多信息，请访问https://docs.djangoproject.com/en/2.0/ref/models/querysets/

class InvoiceResource(resources.ModelResource):

  def get_queryset(self):
      return super().get_queryset().select_related('store_code')
  class Meta:
      model = Invoices