Django：创建扁平化 JSON 的临时表或视图

Question

我们可以创建一个临时表或视图来存储来自 3 或 4 个不同表的数据，并将扁平化的 JSON 而不是嵌套的 JSON 发送到 Django 的前端吗？

我的模型是：

class Place(models.Model):
    id = models.IntegerField(primary_key=True)
    location = models.CharField(max_length=100)

    class Meta:
        db_table = 'place'
        managed=False
        
        
class Session(models.Model):
    id = models.IntegerField(primary_key=True)
    place = models.ForeignKey(Place,related_name='session',on_delete=models.CASCADE, null=True)
    start = models.DateField(auto_now=True)
    counts = models.IntegerField()

    class Meta:
        db_table = 'session'
        managed=False


class Animal(models.Model):
    id = models.IntegerField(primary_key=True)
    sess = models.ForeignKey(Session,related_name='details',on_delete=models.CASCADE, null=True)
    type = models.CharField(max_length=100)
    is_active = models.BooleanField()
    length = models.DecimalField(max_digits=6, decimal_places=2)


    class Meta:
        db_table = 'animal'
        managed=False

我正在尝试的扁平化输出是：

[
    {
        "location": "Loc 1",
        "session_start": "2021-01-01",
        "session_count": 900,
        "session_details_id": 1,
        "session_details_length_max": "22.00",
        "session_details_length_min": "10.00",
        "session_details_length_avg": "16.43",
        "session_details_length_std": "16.00",
        "session_details_is_active": false,
        "session_details_type": "dog"

    },
        "location": "Loc 1",
        "session_start": "2021-01-02",
        "session_count": 400,
        "session_details_id": 2,
        "session_details_length_max": "19.00",
        "session_details_length_min": "12.00",
        "session_details_length_avg": "15.43",
        "session_details_length_std": "13.00",
        "session_details_is_active": false,
        "session_details_type": "dog"
    }
]

而不是我目前得到的嵌套 JSON 数据 嵌套的 JSON 数据是

[
    {
        "location": "Loc 1",
        "session": [
            {
                "start": "2021-01-01",
                "count": 600,
                "details": [
                    {
                        "id": 1,
                        "length_max": "15.00",
                        "length_min": "10.00",
                        "length_avg": "12.00",
                        "length_std": "13.00",
                        "is_active": false,
                        "type": "dog"
                    }
                ]
            },
            {
                "start": "2021-01-02",
                "count": 400,
                "details": [
                    {
                        "id": 2,
                        "length_max": "19.00",
                        "length_min": "12.00",
                        "length_avg": "15.00",
                        "length_std": "13.00",
                        "is_active": true,
                        "type": "dog"
                    }
                ]
            },
            {
                "start": "2021-01-01",
                "count": 300,
                "details": [
                    {
                        "id": 13,
                        "length_max": "22.00",
                        "length_min": "20.00",
                        "length_avg": "20.00",
                        "length_std": "22.00",
                        "is_active": false,
                        "type": "dog"
                    }
                ]
            }
        ]
    }
]

像我们在 SQL 中所做的那样，我们可以在 Django 中创建临时表或视图来存储和展平吗？

Answer 1

您不需要额外的表或临时视图即可。

Here 是一个 SerializerMethodField，我猜你需要什么。例如，在您的用例中，您应该为 Animal 模型创建序列化程序，因为它与 Session 模型相关，而 Session 模型与 Place 模型相关，只需在关系中从下到上，并使用 SerializerMethodField 获取其他字段。

一个小例子：

from rest_framework import serializers


class AnimalSerializer(serializers.ModelSerializer):
    location = serializers.SerializerMethodField()  # You can pass the method argument here, of use the default. If you don't pass this argument your method name should be like `get_<field_name>`, for this field `get_location`
    session_details_type = serializers.SerializerMethodField()
    session_count = serializers.SerializerMethodField()

    def get_location(self, obj):
       return obj.session.place.location

   def get_session_details_type(self, obj):
       return obj.type

   def get_session_count(self, obj):
       # Calculate session count in your way and return it.

您可以添加更多这样的字段并实现您想要的。