如何在 Django ORM 中嵌套两个多对多字段答案

【问题标题】：How to nest two many-to-many fields in Django ORM如何在 Django ORM 中嵌套两个多对多字段
【发布时间】：2021-07-22 00:51:18
【问题描述】：

我有一个表关联两个表，表 Author 和表 Book。

+----+------------+-----------+
| ID | Author(FK) | Book (FK) |
+----+------------+-----------+
|  1 |         20 |        12 |
|  2 |         20 |        35 |
|  3 |         20 |        70 |
|  4 |         25 |        15 |
+----+------------+-----------+

我正在使用序列化程序，我的输出如下所示：

{
  "1": {
    "Author": "20",
    "Book": "12"
  },
  "2": {
    "Author": "20",
    "Book": "35"
  },
  "3": {
    "Author": "20",
    "Book": "70"
  },
  "4": {
    "Author": "25",
    "Book": "15"
  },
}

想要的输出应该是这样的：

[
  {
    "author": 20,
    "books": [
      12,
      35,
      70
    ]
  },
  {
    "author": 25,
    "books": [
      15
    ]
  }
]

这是我的序列化器：

class AuthorBooksSerializer(serializers.ModelSerializer):

    class Meta:
        model = AuthorBooks
        fields = '__all__'

如何将一个作者的所有书籍合并到一个数组中？

【问题讨论】：

请分享你的模型
查看this in the documentation

标签： django django-rest-framework django-orm

【解决方案1】：

使用DRF's PrimaryKeyRelatedField，您可以像这样改进您的AuthorBooksSerializer：

from .models import Book, Author, AuthorBooks

class AuthorBooksSerializer(serializers.ModelSerializer):
    author = serializers.PrimaryKeyRelatedField(read_only=True, queryset=Author.objects.all())
    books = serializers.PrimaryKeyRelatedField(many=True, read_only=True, queryset=Book.objects.all())
    
    class Meta:
        model = AuthorBooks
        fields = '__all__'

奖金

例如，您可以使用Book 模型上的ForeignKey 属性来实现SQL 的Many to One relationship，而不是定义单独的模型AuthorBooks，

from django.db import models
class Book(models.Model):
   # ...snip...
   author = models.ForeignKey(Book, related_name="books", on_delete=models.CASCADE)

然后您可以进行如下查询：

Book.objects.get(1).author # related author instance
Author.objects.get(1).books # list of books

【讨论】：