Django DRF : read_only_fields not working properly

Question

我有以下型号

class Breed(models.Model)::
    name = models.CharField(max_length=200)

class Pet(models.Model):
    owner = models.ForeignKey(
        "User",
        on_delete=models.CASCADE,
    )
    name = models.CharField(max_length=200)
    breed = models.ForeignKey(
        "Breed",
        on_delete=models.CASCADE,
    )

我正在尝试为 representation 添加几个文件目的。我不希望它们包含在 create 中或 update

class PetSerializer(serializers.ModelSerializer):
    owner_email = serializers.CharField(source='owner.email')
    breed_name = serializers.CharField(source='breed.str')
    class Meta:
        model = Pet
        fields = "__all__"
        read_only_fields = ["breed_name","owner_email"]

这是行不通的。我看到了 owner_email和 breed_name在 HTML 表单中(DRF api 页面)
然而

class PetSerializer(serializers.ModelSerializer):
    owner_email = serializers.CharField(source='owner.email',read_only=True)
    breed_name = serializers.CharField(source='breed.str',read_only=True)
    class Meta:
        model = Pet
        fields = "__all__"

这是有效的。我在 HTML 表单中看不到它们
我还观察到，如果我直接在 read_only_fields 中使用模型字段，那么它可以工作。

class PetSerializer(serializers.ModelSerializer):
    class Meta:
        model = Pet
        fields = "__all__"
        read_only_fields = ["name"]

这将使所有 name未在更新或创建中显示
为什么 read_only_fields工作不正常

Answer 1

这是非常有趣的。我查看了代码并找到了根本原因，特别是这个 lines在 ModelSerializer 的实现中:

for field_name in field_names:
    # If the field is explicitly declared on the class then use that.
    if field_name in declared_fields:
        fields[field_name] = declared_fields[field_name]
        continue

    ....

这是我的调查脚本

from django.db import models
from rest_framework import serializers


class MyModel(models.Model):
    xero_contact_id = models.UUIDField(unique=True)
    name = models.CharField(max_length=255, default="Some name")
    class Meta:
        db_table = "my_model"


class MySerializer(serializers.ModelSerializer):
    owner_email = serializers.CharField()
    breed_name = serializers.CharField(max_length=255)
    class Meta:
        model = MyModel
        fields = '__all__'
        read_only_fields = ["breed_name", "owner_email", "xero_contact_id"]


serializer = MySerializer()
print(repr(serializer))

我添加了一些打印品，这是我看到的:

>>> print(repr(serializer))
field_names ['id', 'owner_email', 'breed_name', 'xero_contact_id', 'name']
declared_fields OrderedDict([('owner_email', CharField()), ('breed_name', CharField(max_length=255))])
extra_kwargs {'breed_name': {'read_only': True}, 'owner_email': {'read_only': True}, 'xero_contact_id': {'read_only': True}}
MySerializer():
    id = IntegerField(label='ID', read_only=True)
    owner_email = CharField()
    breed_name = CharField(max_length=255)
    xero_contact_id = UUIDField(read_only=True)
    name = CharField(max_length=255, required=False)

如您所见， read_only参数在 extra_kwargs 中.问题是对于所有仅在 ModelSerializer 中声明的字段本身(从 declared_fields 可见)而不是在模型类中，它们不从 extra_kwargs 读取，他们只是读取了字段本身设置的内容，如上面的代码片段 fields[field_name] = declared_fields[field_name] 所示然后执行 continue .因此， read_only 的选项被忽略了。
我通过修改 ModelSerializer 的实现来修复它还要考虑 extra_kwargs即使对于非模型字段

for field_name in field_names:
    # If the field is explicitly declared on the class then use that.
    if field_name in declared_fields:
        field_class = type(declared_fields[field_name])
        declared_field_args = declared_fields[field_name].__dict__['_args']
        declared_field_kwargs = declared_fields[field_name].__dict__['_kwargs']
        extra_field_kwargs = extra_kwargs.get(field_name, {})

        # Old implementation doesn't take into account the extra_kwargs
        # fields[field_name] = declared_fields[field_name]

        # New implementation takes into account the extra_kwargs
        fields[field_name] = field_class(*declared_field_args, **declared_field_kwargs, **extra_field_kwargs)
        continue

    ....

现在， read_only已正确设置为目标字段，包括非模型字段:

>>> print(repr(serializer))
field_names ['id', 'owner_email', 'breed_name', 'xero_contact_id', 'name']
declared_fields OrderedDict([('owner_email', CharField()), ('breed_name', CharField(max_length=255))])
extra_kwargs {'breed_name': {'read_only': True}, 'owner_email': {'read_only': True}, 'xero_contact_id': {'read_only': True}}
MySerializer():
    id = IntegerField(label='ID', read_only=True)
    owner_email = CharField(read_only=True)
    breed_name = CharField(max_length=255, read_only=True)
    xero_contact_id = UUIDField(read_only=True)
    name = CharField(max_length=255, required=False)

这似乎不在 DRF 文档中。听起来像是我们可以向 DRF 请求的功能 :) 所以在此期间的解决方案是@JPG 指出的，使用 read_only=True在额外的非模型字段中明确显示。