Question

我有两个型号：

class Company(models.Model):
    ...

class Supplier(models.Model):
  company = models.ForeignKey(Company, null=True, related_name="suppliers")

如何让所有公司与其相关供应商合作？

我试过了：

Company.objects.prefetch_related('suppliers') 
Company.objects.prefetch_related('supplier_set') 
Company.objects.prefetch_related('suppliers').all()
...

我做错了什么？

谢谢

Answer 1

prefetch_related just adds the SQL query让供应商在company.suppliers.all()执行Company.objects.all()时，不会在companies = Company.objects.all().prefetch_related('suppliers') for company in companies: # Does not require a new SQL query suppliers = company.suppliers.all()之上发生另一次SQL命中。您可以在此后访问供应商：

    # Some Data. All rows have an NA but not all columns

    df <- data.frame(col1 = c(NA, 2, 3, 4),
             col2 = c(1, NA, 3, 4),
             col3 = c(1, 2, NA, 4),
             col4 = c(1, 2, 3, NA),
             col5 = c(1, 2, 3, 4))

# test whether an NA is present in each row

apply(df, 1, function(x) {sum(is.na(x)) > 0})
[1] TRUE TRUE TRUE TRUE

prefetch_related（）Django中的ForeignKey反向查找？

1 个答案: