如何在 Django 中内部连接 ​​4 个表？

Question

我们想一次检索所有表记录如何在 django orm 中实现类似 SQL 查询。

示例 SQL 查询：

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

您可以为此使用prefetch_related ，如评论中所述：

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

事实上，这不会执行 SQL INNER JOIN，但会在 Python 级别连接预取对象 - 这将减少使用相关对象字段时对 DB 的命中。