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问题:
Problem
As recommended in the blogpost Best Practices for Designing a Pragmatic RESTful API, I would like to add a fields query parameter to a Django Rest Framework based API which enables the user to select only a subset of fields per resource.
Example
Serializer:
class IdentitySerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = models.Identity
fields = ('id', 'url', 'type', 'data')
A regular query would return all fields.
GET /identities/
[
{
"id": 1,
"url": "http://localhost:8000/api/identities/1/",
"type": 5,
"data": "John Doe"
},
...
]
A query with the fields parameter should only return a subset of the fields:
GET /identities/?fields=id,data
[
{
"id": 1,
"data": "John Doe"
},
...
]
A query with invalid fields should either ignore the invalid fields or throw a client error.
Goal
Is this possible out of the box somehow? If not, what's the simplest way to implement this? Is there a 3rd party package around that does this already?
回答1:
You can override the serializer __init__ method and set the fields attribute dynamically, based on the query params. You can access the request object throughout the context, passed to the serializer.
Here is a copy&paste from Django Rest Framework documentation example on the matter:
from rest_framework import serializers
class DynamicFieldsModelSerializer(serializers.ModelSerializer):
"""
A ModelSerializer that takes an additional `fields` argument that
controls which fields should be displayed.
"""
def __init__(self, *args, **kwargs):
# Instantiate the superclass normally
super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)
fields = self.context['request'].query_params.get('fields')
if fields:
fields = fields.split(',')
# Drop any fields that are not specified in the `fields` argument.
allowed = set(fields)
existing = set(self.fields.keys())
for field_name in existing - allowed:
self.fields.pop(field_name)
class UserSerializer(DynamicFieldsModelSerializer, serializers.HyperlinkedModelSerializer):
class Meta:
model = User
fields = ('url', 'username', 'email')
回答2:
This functionality is available from a 3rd-party package.
pip install djangorestframework-queryfields
Declare your serializer like this:
from rest_framework.serializers import ModelSerializer
from drf_queryfields import QueryFieldsMixin
class MyModelSerializer(QueryFieldsMixin, ModelSerializer):
...
Then the fields can now be specified (client-side) by using query arguments:
GET /identities/?fields=id,data
Exclusion filtering is also possible, e.g. to return every field except id:
GET /identities/?fields!=id
disclaimer: I'm the author/maintainer.
回答3:
serializers.py
class DynamicFieldsSerializerMixin(object):
def __init__(self, *args, **kwargs):
# Don't pass the 'fields' arg up to the superclass
fields = kwargs.pop('fields', None)
# Instantiate the superclass normally
super(DynamicFieldsSerializerMixin, self).__init__(*args, **kwargs)
if fields is not None:
# Drop any fields that are not specified in the `fields` argument.
allowed = set(fields)
existing = set(self.fields.keys())
for field_name in existing - allowed:
self.fields.pop(field_name)
class UserSerializer(DynamicFieldsSerializerMixin, serializers.HyperlinkedModelSerializer):
password = serializers.CharField(
style={'input_type': 'password'}, write_only=True
)
class Meta:
model = User
fields = ('id', 'username', 'password', 'email', 'first_name', 'last_name')
def create(self, validated_data):
user = User.objects.create(
username=validated_data['username'],
email=validated_data['email'],
first_name=validated_data['first_name'],
last_name=validated_data['last_name']
)
user.set_password(validated_data['password'])
user.save()
return user
views.py
class DynamicFieldsViewMixin(object):
def get_serializer(self, *args, **kwargs):
serializer_class = self.get_serializer_class()
fields = None
if self.request.method == 'GET':
query_fields = self.request.QUERY_PARAMS.get("fields", None)
if query_fields:
fields = tuple(query_fields.split(','))
kwargs['context'] = self.get_serializer_context()
kwargs['fields'] = fields
return serializer_class(*args, **kwargs)
class UserList(DynamicFieldsViewMixin, ListCreateAPIView):
queryset = User.objects.all()
serializer_class = UserSerializer
回答4:
Configure a new pagination serializer class
from rest_framework import pagination, serializers
class DynamicFieldsPaginationSerializer(pagination.BasePaginationSerializer):
"""
A dynamic fields implementation of a pagination serializer.
"""
count = serializers.Field(source='paginator.count')
next = pagination.NextPageField(source='*')
previous = pagination.PreviousPageField(source='*')
def __init__(self, *args, **kwargs):
"""
Override init to add in the object serializer field on-the-fly.
"""
fields = kwargs.pop('fields', None)
super(pagination.BasePaginationSerializer, self).__init__(*args, **kwargs)
results_field = self.results_field
object_serializer = self.opts.object_serializer_class
if 'context' in kwargs:
context_kwarg = {'context': kwargs['context']}
else:
context_kwarg = {}
if fields:
context_kwarg.update({'fields': fields})
self.fields[results_field] = object_serializer(source='object_list',
many=True,
**context_kwarg)
# Set the pagination serializer setting
REST_FRAMEWORK = {
# [...]
'DEFAULT_PAGINATION_SERIALIZER_CLASS': 'DynamicFieldsPaginationSerializer',
}
Make dynamic serializer
from rest_framework import serializers
class DynamicFieldsModelSerializer(serializers.ModelSerializer):
"""
A ModelSerializer that takes an additional `fields` argument that
controls which fields should be displayed.
See:
http://tomchristie.github.io/rest-framework-2-docs/api-guide/serializers
"""
def __init__(self, *args, **kwargs):
# Don't pass the 'fields' arg up to the superclass
fields = kwargs.pop('fields', None)
# Instantiate the superclass normally
super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)
if fields:
# Drop any fields that are not specified in the `fields` argument.
allowed = set(fields)
existing = set(self.fields.keys())
for field_name in existing - allowed:
self.fields.pop(field_name)
# Use it
class MyPonySerializer(DynamicFieldsModelSerializer):
# [...]
Last, use a homemage mixin for your APIViews
class DynamicFields(object):
"""A mixins that allows the query builder to display certain fields"""
def get_fields_to_display(self):
fields = self.request.GET.get('fields', None)
return fields.split(',') if fields else None
def get_serializer(self, instance=None, data=None, files=None, many=False,
partial=False, allow_add_remove=False):
"""
Return the serializer instance that should be used for validating and
deserializing input, and for serializing output.
"""
serializer_class = self.get_serializer_class()
context = self.get_serializer_context()
fields = self.get_fields_to_display()
return serializer_class(instance, data=data, files=files,
many=many, partial=partial,
allow_add_remove=allow_add_remove,
context=context, fields=fields)
def get_pagination_serializer(self, page):
"""
Return a serializer instance to use with paginated data.
"""
class SerializerClass(self.pagination_serializer_class):
class Meta:
object_serializer_class = self.get_serializer_class()
pagination_serializer_class = SerializerClass
context = self.get_serializer_context()
fields = self.get_fields_to_display()
return pagination_serializer_class(instance=page, context=context, fields=fields)
class MyPonyList(DynamicFields, generics.ListAPIView):
# [...]
Request
Now, when you request a resource, you can add a parameter fields to show only specified fields in url.
/?fields=field1,field2
You can find a reminder here : https://gist.github.com/Kmaschta/e28cf21fb3f0b90c597a
回答5:
Such functionality we've provided in drf_tweaks / control-over-serialized-fields.
If you use our serializers, all you need is to pass ?fields=x,y,z parameter in the query.
回答6:
You could try Dynamic REST, which has support for dynamic fields (inclusion, exclusion), embedded / sideloaded objects, filtering, ordering, pagination, and more.
回答7:
For nested data, I am using Django Rest Framework with the package recommended in the docs, drf-flexfields
This allows you to restrict the fields returned on both the parent and child objects. The instructions in the readme are good, just a few things to watch out for:
The URL seems to need the / like this '/person/?expand=country&fields=id,name,country' instead of as written in the readme '/person?expand=country&fields=id,name,country'
The naming of the nested object and its related name need to be completely consistent, which isn't required otherwise.
If you have 'many' e.g. a country can have many states, you'll need to set 'many': True in the Serializer as described in the docs.
回答8:
If you want something flexible like GraphQL, you can use django-restql. It supports nested data (both flat and iterable).
Example
from rest_framework import serializers
from django.contrib.auth.models import User
from django_restql.mixins import DynamicFieldsMixin
class UserSerializer(DynamicFieldsMixin, serializers.ModelSerializer):
class Meta:
model = User
fields = ('id', 'username', 'email', 'groups')
A regular request returns all fields.
GET /users
[
{
"id": 1,
"username": "yezyilomo",
"email": "yezileliilomo@hotmail.com",
"groups": [1,2]
},
...
]
A request with the query parameter on the other hand returns only a subset of
the fields:
GET /users/?query={id, username}
[
{
"id": 1,
"username": "yezyilomo"
},
...
]
With django-restql you can access nested fields of any level. E.g
GET /users/?query={id, username, date_joined{year}}
[
{
"id": 1,
"username": "yezyilomo",
"date_joined": {
"year": 2018
}
},
...
]
For iterable nested fields, E.g groups on users.
GET /users/?query={id, username, groups{id, name}}
[
{
"id": 1,
"username": "yezyilomo",
"groups": [
{
"id": 2,
"name": "Auth_User"
}
]
},
...
]
