[英]Joining Multiple Tables in Django
I have looked through around and there doesn't seem to be anything that has exactly answered what I am looking for, using the following model I want to join all the tables: 我浏览了一下,似乎没有什么可以完全满足我所寻找的东西,使用下面的模型,我想连接所有表:
class A(models.Model):
name = models.CharField(max_length=60)
class B(models.Model):
a = models.ForeignField(A)
class C(models.Model):
a = models.ForeignField(A)
class D(models.Model):
a = models.ForeignField(A)
This is a very basic sort of structure I have going on, I want to join all the tables based on there foreign key link the A. I have looked at select_related but it seems like that is the reverse direction of what I want to do because it links an object to what it references and I want to join based on what references it. 这是我正在进行的一种非常基本的结构,我想基于那里的外键链接A来连接所有表。我已经看过select_related了,但这似乎是我想要做的事情的反向它将对象链接到它所引用的对象,我想根据引用的对象来加入。
Basically I want to join the tables like this MySQL query: 基本上我想像这样的MySQL查询联接表:
SELECT * FROM A, B, C, D WHERE A.id = B.aID AND A.id = C.aID AND A.id = D.aID;
You can use a custom join for your purpose: 您可以根据需要使用自定义联接 :
# assume our models.py contains the following
class Contact(models.Model):
name = models.CharField(max_length=255)
phones = models.ManyToManyField('Phone')
addresses = models.ManyToManyField('Address')
class Phone(models.Model):
number = models.CharField(max_length=16)
# join as follows
contacts = Contact.objects.extra(
select={'phone': 'crm_phone.number'}
).order_by('name')
# setup intial FROM clause
# OR contacts.query.get_initial_alias()
contacts.query.join((None, 'crm_contact', None, None))
# join to crm_contact_phones
connection = (
'crm_contact',
'crm_contact_phones',
'id',
'contact_id',
)
contacts.query.join(connection, promote=True)
# join to crm_phone
connection = (
'crm_contact_phones',
'crm_phone',
'phone_id',
'id',
)
contacts.query.join(connection, promote=True)
Wash, rinse, repeat for every pair of tables till you're happy. 清洗,漂洗,对每对桌子重复,直到您感到满意为止。 If this is too involved, you can always use custom SQL .
如果涉及的过多,则始终可以使用自定义SQL 。
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