如何在 Django 中內部連接 ​​4 個表？

Question

我們想一次檢索所有表記錄如何在 django orm 中實現類似 SQL 查詢。

示例 SQL 查詢：

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

代碼：

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

您可以為此使用prefetch_related ，如評論中所述：

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

事實上，這不會執行 SQL INNER JOIN，但會在 Python 級別連接預取對象 - 這將減少使用相關對象字段時對 DB 的命中。