python - 如何在Django中内连接4个表？

Question

我们想要一次检索所有表记录，如何在django orm中实现类似SQL查询。

SQL 查询示例:

select * 
from Company_info 
inner join Bank_info on Bank_info.manufacturer = Company_info.manufacturer
inner join Company_info on Company_info.manufacturer = Company_info.manufacturer
inner join Transport_info on Transport_info.manufacturer = Company_info.manufacturer

代码:

class Manufacturer(models.Model):
    name = models.CharField(max_length=42)

class Bank_info(models.Model):
    account = models.CharField(max_length=42)
    manufacturer = models.ForeignKey(Manufacturer, on_delete= models.CASCADE)

class Company_info(models.Model):
    name= models.CharField(max_length=42)
    manufacturer = models.ForeignKey(Manufacturer, on_delete= models.CASCADE)

class Transport_info(models.Model):
    name= models.CharField(max_length=42)
    manufacturer = models.ForeignKey(Manufacturer, on_delete= models.CASCADE)

Answer 1

您可以使用prefetch_related为此，正如评论中提到的:

Manufacturer.objects.all().prefetch_related('related_name2', 'related_name3', 'related_name4')

事实上，这不会执行 SQL INNER JOIN，而是会在 Python 级别连接预取的对象 - 这将减少使用相关对象字段时对数据库的命中。