Python 没有外键的 Django-queryset 连接
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Django-queryset join without foreignkey
提问by luzik
model.py
模型.py
class Tdzien(models.Model):
dziens = models.SmallIntegerField(primary_key=True, db_column='DZIENS')
dzienrok = models.SmallIntegerField(unique=True, db_column='ROK')
class Tnogahist(models.Model):
id_noga = models.ForeignKey(Tenerg, primary_key=True, db_column='ID_ENERG')
dziens = models.SmallIntegerField(db_column='DZIENS')
What I want is to get id_noga where dzienrok=1234. I know that dziens should be
我想要的是在 dzienrok=1234 处获得 id_noga。我知道 dziens 应该是
dziens = models.ForeignKey(Tdzien)
but it isn't and I can't change that. Normally I would use something like
但事实并非如此，我无法改变这一点。通常我会使用类似的东西
Tnogahist.objects.filter(dziens__dzienrok=1234)
but I don't know how to join and filter those tables without foreignkey.
但我不知道如何在没有外键的情况下加入和过滤这些表。
采纳答案by Lucas
It's possible to join two tables by performing a raw sql query. But for this case it's quite nasty, so I recommend you to rewrite your models.py.
可以通过执行原始 sql 查询来连接两个表。但是对于这种情况，它很讨厌，所以我建议你重写你的models.py。
You can check how to do this here
您可以在此处查看如何执行此操作
It would be something like this:
它会是这样的：
from django.db import connection
def my_custom_sql(self):
cursor = connection.cursor()
cursor.execute("select id_noga
from myapp_Tnogahist a
inner join myapp_Tdzien b on a.dziens=b.dziens
where b.dzienrok = 1234")
row = cursor.fetchone()
return row
回答by RemcoGerlich
No joins without a foreign key as far as I know, but you could use two queries:
据我所知，没有外键就没有连接，但您可以使用两个查询：
Tnogahist.objects.filter(dziens__in=Tdzien.objects.filter(dzienrok=1234))
Tnogahist.objects.filter(dziens__in=Tdzien.objects.filter(dzienrok=1234))
回答by Paul Tomblin
Could you do this with .extra? From https://docs.djangoproject.com/en/dev/ref/models/querysets/#extra:
你能做到这一点.extra吗？从https://docs.djangoproject.com/en/dev/ref/models/querysets/#extra：
where / tables
You can define explicit SQL WHERE clauses — perhaps to perform non-explicit joins — by using where. You can manually add tables to the SQL FROM clause by using tables.
哪里/表
您可以使用 where 定义显式 SQL WHERE 子句——也许是为了执行非显式连接。您可以使用表手动向 SQL FROM 子句添加表。
