django访问原始许多创建的表字段 [英] django accessing raw many to many created table fields

问题描述

型号：

class Subjects (models.Model):
    name = models.CharField(max_length=100)
    places = models.CharField(max_length=100)


class Student (models.Model):
    name = models.CharField(max_length=40)
    lastname = models.CharField(max_length=80)
    subjects = models.ManyToManyField(Subjects, blank=True)

当我使用上面的模型时，Django会创建appname_student_subjects。

Django creates appname_student_subjects when I use model above.

appname_student_subjects表如下所示：

appname_student_subjects table looks for example, like this:

id   |    student_id   |  subjects_id
-----------------------------------------
1    |    1            |  10
2    |    4            |  11
3    |    4            |  19
4    |    5            |  10
...
~1000

如何访问subjects_id字段和计算上面表格中存在subject_id的次数（然后用它做一些事情）。例如：如果ID为10的对象存在两次模板显示2.我知道我应该使用len结果，但是我不知道如何访问subject_id字段。
用外键我在一个for循环中这样做：

How can I access subjects_id field and count how many times subjects_id exists in the table above (and then do something with it). For example: If subject with id 10 exists two times the template displays 2. I know that I should use "len" with result but i don't know how to access subject_id field. With foreign keys I'm doing it like this in a for loop:

results_all = Students.objects.filter(subject_id='10')
result = len(results_all)

到模板并在for循环中显示它，但它不是外键，所以它不工作。

and I pass result to the template and display it within a for loop but it's not a foreign key so it's not working.

推荐答案

您可以访问直接通过表。

You can access the through table directly.

num = (Students.subjects  # M2M Manager
               .through  # subjects_students through table
               .objects  # through table manager
               .filter(student_id=10)  # your query against through table
               .count())

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