如何在Django 1.11

Question

如何在Django 1.11中进行加入声明， 我想创建此语句：

select t1.name ,t2.str, t2.num
from table_1 as t1
join table_2 as t2 on t2.product_id = t1.id and t2.section_num = 2;

the models:


class t1(UTModelTS):
    alt_keys = product_alt_keys
    name = utCharField()
    ...

class t2(UTModelTS):
    alt_keys= [('pr_id', 'section')]    
    str = utCharField()
    num = models.IntegerField()

    ...

我尝试过

 t1 = t1.objects.filter(**params).exclude(**exclude)
 t1 = t1.select_related('t2')
`

但是我可以在哪里添加on语句？

注意-联接不是通过外键

Answer 1

不，不幸的是，没有一种有效/优雅的方法。

尽管您可以使用.raw()/RawSQL()方法执行此操作。即使可能，它也可能比原始SQL慢很多。 https://docs.djangoproject.com/en/2.2/topics/db/sql/

Answer 2

您不应添加on语句。 Django的 ORM将自动为您执行内部联接。

想象一下这是我们的模型。用户表和发布表。

class User(models.Model):
    name = models.CharField(max_length=30)
    surname = models.CharField(max_length=50)


class Post(models.Model):
    title = models.CharField(max_length=50)
    text = models.TextField()
    user = models.ForeignKey(to='User', on_delete=models.CASCADE) # this is FK field to users

用法

qs = Post.objects.select_related('user') # This will performs SQL INNER JOIN.
print(qs.query) # use query attribute to show what query is performed.

这将生成SQL查询

SELECT "myapp_post"."id", "myapp_post"."title", "myapp_post"."text", "myapp_post"."user_id", "myapp_user"."id", "myapp_user"."name", "myapp_user"."surname" FROM "myapp_post" INNER JOIN "myapp_user" ON ("myapp_post"."user_id" = "myapp_user"."id")

查看您的模型，

class t1(UTModelTS):
    alt_keys = product_alt_keys
    name = utCharField()
    t2 = models.ForeignKey(to='t2', on_delete=models.CASCADE)

class t2(UTModelTS):
    alt_keys= [('pr_id', 'section')]    
    str = utCharField()
    num = models.IntegerField()

将t2 FK添加到您的t1模型中。

查询

qs = t1.objects.select_related('t2')

OR

qs = t1.objects.select_related('t2').filter(**lookup_kwargs).

select_related()返回QuerySet对象，您可以在QuerySet之后使用select_related()方法。