django：我如何根据GenericForeignKey的字段进行查询？ [英] django: how do I query based on GenericForeignKey's fields?

问题描述

我是使用GenericForeignKey的新功能，我无法使其在查询语句中工作。表格大致如下：

I'm new in using GenericForeignKey, and I couldn't make it to work in a query statement. The tables are roughly like the following:

class Ticket(models.Model):
    issue_ct = models.ForeignKey(ContentType, related_name='issue_content_type')
    issue_id = models.PositiveIntegerField(null=True, blank=True)
    issue = generic.GenericForeignKey('issue_ct', 'issue_id')

class Issue(models.Model):
    scan = models.ForeignKey(Scan)

扫描会创建一个问题，一个问题会生成一些票证，而且我将问题作为票证表的外键。现在我有一个扫描对象，我想查询与此扫描相关的所有票证。我先试了一下：

A scan creates one issue, an issue generates some tickets, and I made Issue as a foreign key to Ticket table. Now I have a Scan object, and I want to query for all the tickets that related to this scan. I tried this first:

tickets = Tickets.objects.filter(issue__scan=scan_obj)

哪些不起作用然后我尝试这样：

which doesn't work. Then I tried this:

issue = Issue.objects.get(scan=scan_obj)
content_type = ContentType.objects.get_for_model(Issue)
tickets = Tickets.objects.filter(content_type=content_type, issue=issue)

仍然不行。我需要知道如何在django中进行这些查询？谢谢。

Still doesn't work. I need to know how to do these kind of queries in django? Thanks.

推荐答案

您定义的 Ticket.issue 字段帮助您从 Ticket 实例转到附加到的问题，但不会让您退后。你与第二个例子相近，但你需要使用 issue_id 字段 - 你不能在 GenericForeignKey （当您有 Ticket 实例）时，它只会帮助您检索对象。尝试这样：

The Ticket.issue field you've defined will help you go from a Ticket instance to the Issue it's attached to, but it won't let you go backwards. You're close with your second example, but you need to use the issue_id field - you can't query on the GenericForeignKey (it just helps you retrieve the object when you have a Ticket instance). Try this:

from django.contrib.contenttypes.models import ContentType

issue = Issue.objects.get(scan=scan_obj)
tickets = Ticket.objects.filter(issue_id=issue.id, issue_ct=ContentType.objects.get_for_model(issue))

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