如何在 Django 查询集中进行左连接

Question

我有两个模型，我需要做一个左连接操作我尝试了一些解决方案，但还没有成功

型号

class SmdRepairIn(models.Model):
    sum_ymd = models.DateField(blank=True, null=True)
    line_nm = models.CharField(max_length=20, blank=True, null=True)
    model_code = models.CharField(max_length=20, blank=True, null=True)

class SmdRepairOut(models.Model):  
    repair_in_id = models.CharField(max_length=20, blank=True, null=True)  
    repairman_out = models.CharField(max_length=30, blank=True, null=True)

SMDRepairIn.id == SmdRepairOut.repair_in_id

我要检索对应的查询结果：

select A.*, B.repairman_out 
from SmdRepairIn as A
     left join (select repairman_out from SmdRepairOut) B on (A.id = B.repair_in_id )

如何在django queryset中实现？

预期结果应该是：

id, sum_ymd, line_nm, model_code, repairmain_out

Answer 1

您应该在模型中使用 Foreignkey：

class SmdRepairIn(models.Model):
    sum_ymd = models.DateField(blank=True, null=True)
    line_nm = models.CharField(max_length=20, blank=True, null=True)
    model_code = models.CharField(max_length=20, blank=True, null=True)

class SmdRepairOut(models.Model):  
    repair_in = models.ForeignKey(SmdRepairIn, blank=True, null=True, on_delete=models.SET_NULL)  
    repairman_out = models.CharField(max_length=30, blank=True, null=True)

(注意：你应该重新考虑是否有一个没有SmdRepairIn的SmdRepairOut。如果没有，ForeignKey行应该是repair_in = models.ForeignKey(SmdRepairIn, on_delete=models.CASCADE))

这将允许您查询所需的选择。示例见此处：https://docs.djangoproject.com/en/3.2/topics/db/examples/many_to_one/

一些示例：

SmdRepairIn.objects.all().values_list('sum_ymd', 'line_nm', 'model_code', 'smdrepairout__repairman_out')

这与您的要求很接近。它使用反向查找 smdrepairout__repairman_out.

反过来说：

SmdRepairOut.objects.all().values_list('repairman_out', 'repair_in__sum_ymd')

如何在 Django 查询集中进行左连接

How to make a left join in django queryset

django

django-models

django-queryset