将 Django 模型对象转换为 dict 并且所有字段都完好无损

  
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问题描述

如何将 django 模型对象转换为具有 所有 字段的字典?理想情况下，所有内容都包括外键和具有可编辑=False 的字段.

How does one convert a django Model object to a dict with all of its fields? All ideally includes foreign keys and fields with editable=False.

让我详细说明.假设我有一个 django 模型，如下所示:

Let me elaborate. Let's say I have a django model like the following:

from django.db import models

class OtherModel(models.Model): pass

class SomeModel(models.Model):
    normal_value = models.IntegerField()
    readonly_value = models.IntegerField(editable=False)
    auto_now_add = models.DateTimeField(auto_now_add=True)
    foreign_key = models.ForeignKey(OtherModel, related_name="ref1")
    many_to_many = models.ManyToManyField(OtherModel, related_name="ref2")

在终端中，我做了以下事情:

In the terminal, I have done the following:

other_model = OtherModel()
other_model.save()
instance = SomeModel()
instance.normal_value = 1
instance.readonly_value = 2
instance.foreign_key = other_model
instance.save()
instance.many_to_many.add(other_model)
instance.save()

我想把它转换成下面的字典:

I want to convert this to the following dictionary:

{'auto_now_add': datetime.datetime(2015, 3, 16, 21, 34, 14, 926738, tzinfo=<UTC>),
 'foreign_key': 1,
 'id': 1,
 'many_to_many': [1],
 'normal_value': 1,
 'readonly_value': 2}

回答不满意的问题:

Questions with unsatisfactory answers:

Django:转换整个模型的对象集合到一个字典中

如何将 Django 模型对象转换为字典并且仍然拥有它们的外键?

推荐答案

有很多方法可以将实例转换为字典，不同程度的极端情况处理和接近所需结果.

There are many ways to convert an instance to a dictionary, with varying degrees of corner case handling and closeness to the desired result.

instance.__dict__

返回

{'_foreign_key_cache': <OtherModel: OtherModel object>,
 '_state': <django.db.models.base.ModelState at 0x7ff0993f6908>,
 'auto_now_add': datetime.datetime(2018, 12, 20, 21, 34, 29, 494827, tzinfo=<UTC>),
 'foreign_key_id': 2,
 'id': 1,
 'normal_value': 1,
 'readonly_value': 2}

这是迄今为止最简单的，但缺少 many_to_many，foreign_key 名称错误，其中包含两个不需要的额外内容.

This is by far the simplest, but is missing many_to_many, foreign_key is misnamed, and it has two unwanted extra things in it.

from django.forms.models import model_to_dict
model_to_dict(instance)

返回

{'foreign_key': 2,
 'id': 1,
 'many_to_many': [<OtherModel: OtherModel object>],
 'normal_value': 1}

这是唯一一个有 many_to_many 的，但缺少不可编辑的字段.

This is the only one with many_to_many, but is missing the uneditable fields.

from django.forms.models import model_to_dict
model_to_dict(instance, fields=[field.name for field in instance._meta.fields])

返回

{'foreign_key': 2, 'id': 1, 'normal_value': 1}

这比标准的 model_to_dict 调用更糟糕.

This is strictly worse than the standard model_to_dict invocation.

SomeModel.objects.filter(id=instance.id).values()[0]

返回

{'auto_now_add': datetime.datetime(2018, 12, 20, 21, 34, 29, 494827, tzinfo=<UTC>),
 'foreign_key_id': 2,
 'id': 1,
 'normal_value': 1,
 'readonly_value': 2}

这与 instance.__dict__ 的输出相同，但没有额外的字段.foreign_key_id 仍然错误，many_to_many 仍然缺失.

This is the same output as instance.__dict__ but without the extra fields. foreign_key_id is still wrong and many_to_many is still missing.

django 的 model_to_dict 的代码给出了大部分答案.它显式删除了不可编辑的字段，因此删除该检查并获取多对多字段的外键 id 会导致以下代码按预期运行:

The code for django's model_to_dict had most of the answer. It explicitly removed non-editable fields, so removing that check and getting the ids of foreign keys for many to many fields results in the following code which behaves as desired:

from itertools import chain

def to_dict(instance):
    opts = instance._meta
    data = {}
    for f in chain(opts.concrete_fields, opts.private_fields):
        data[f.name] = f.value_from_object(instance)
    for f in opts.many_to_many:
        data[f.name] = [i.id for i in f.value_from_object(instance)]
    return data

虽然这是最复杂的选项，但调用 to_dict(instance) 可以为我们提供准确的结果:

While this is the most complicated option, calling to_dict(instance) gives us exactly the desired result:

{'auto_now_add': datetime.datetime(2018, 12, 20, 21, 34, 29, 494827, tzinfo=<UTC>),
 'foreign_key': 2,
 'id': 1,
 'many_to_many': [2],
 'normal_value': 1,
 'readonly_value': 2}

<小时>

6.使用序列化器

Django Rest Framework 的 ModelSerialzer 允许您从模型自动构建序列化程序.

6. Use Serializers

Django Rest Framework's ModelSerialzer allows you to build a serializer automatically from a model.

from rest_framework import serializers
class SomeModelSerializer(serializers.ModelSerializer):
    class Meta:
        model = SomeModel
        fields = "__all__"

SomeModelSerializer(instance).data

返回

{'auto_now_add': '2018-12-20T21:34:29.494827Z',
 'foreign_key': 2,
 'id': 1,
 'many_to_many': [2],
 'normal_value': 1,
 'readonly_value': 2}

这几乎和自定义函数一样好，但是 auto_now_add 是一个字符串而不是一个日期时间对象.

This is almost as good as the custom function, but auto_now_add is a string instead of a datetime object.

如果你想要一个有更好的 python 命令行显示的 django 模型，让你的模型子类如下:

If you want a django model that has a better python command-line display, have your models child-class the following:

from django.db import models
from itertools import chain

class PrintableModel(models.Model):
    def __repr__(self):
        return str(self.to_dict())

    def to_dict(instance):
        opts = instance._meta
        data = {}
        for f in chain(opts.concrete_fields, opts.private_fields):
            data[f.name] = f.value_from_object(instance)
        for f in opts.many_to_many:
            data[f.name] = [i.id for i in f.value_from_object(instance)]
        return data

    class Meta:
        abstract = True

例如，如果我们这样定义模型:

So, for example, if we define our models as such:

class OtherModel(PrintableModel): pass

class SomeModel(PrintableModel):
    normal_value = models.IntegerField()
    readonly_value = models.IntegerField(editable=False)
    auto_now_add = models.DateTimeField(auto_now_add=True)
    foreign_key = models.ForeignKey(OtherModel, related_name="ref1")
    many_to_many = models.ManyToManyField(OtherModel, related_name="ref2")

调用 SomeModel.objects.first() 现在会给出如下输出:

Calling SomeModel.objects.first() now gives output like this:

{'auto_now_add': datetime.datetime(2018, 12, 20, 21, 34, 29, 494827, tzinfo=<UTC>),
 'foreign_key': 2,
 'id': 1,
 'many_to_many': [2],
 'normal_value': 1,
 'readonly_value': 2}

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