from datetime import datetime

class Comment(object):
    def __init__(self, email, content, created=None):
        self.email = email
        self.content = content
        self.created = created or datetime.now()

from rest_framework import serializers

class CommentSerializer(serializers.Serializer):
    email = serializers.EmailField()
    content = serializers.CharField(max_length=200)
    created = serializers.DateTimeField()

    def create(self, validated_data):
        return Comment(**validated_data)

    def update(self, instance, validated_data):
        instance.email = validated_data.get('email', instance.email)
        instance.content = validated_data.get('content', instance.content)
        instance.created = validated_data.get('created', instance.created)
        return instance

comment = Comment(email='leila@example.com', content='fooooo')

# .save() will create a new instance.
serializer = CommentSerializer(data=data)

# .save() will update the existing `comment` instance.
serializer = CommentSerializer(comment, data=data)

from django.contrib.auth.models import User
from django.contrib.auth.hashers import make_password
from rest_framework import serializers


class UserSerializer(serializers.ModelSerializer):
    # SerializerMethodField は get_xxxx ってなっているメソッドをコールする
    full_name = serializers.SerializerMethodField()

    class Meta:
        model = User
        fields = ('username', 'email', 'first_name', 'last_name', 'full_name')
        extra_kwargs = {
            'username': {'read_only': True},
            'password': {'write_only': True},
        }

    def get_full_name(self, instance):
        return instance.get_full_name()  # User に元からあるメソッドを呼び出してるだけ

    def create(self, validated_data):
        password = validated_data.pop('password', 'something')  # そのまま使っちゃだめだよ
        user = User(username=uuid.uuid4().hex, password=make_password(password), **validated_data)
        user.save()
        return user

>>> serializer = UserSerializer(data={'first_name': 'Takanori', 'last_name': 'Shimizukawa', 'username': 'test', 'email': 'test@example.com'})
>>> serializer.is_valid()
True
>>> u = serializer.save()
>>> serializer.data  # だれだろうこれ
{'username': '4d46f60c84be4ae09090bb1751b9e289',
 'email': 'test@example.com',
 'first_name': 'Takanori',
 'last_name': 'Shimizukawa',
 'full_name': 'Takanori Shimizukawa'}
# 間違っていたので partial で名前だけを指定して修正
>>> serializer2 = UserSerializer(u, data={'first_name': 'Takayuki'}, partial=True)
>>> serializer2.is_valid()
True
>>> u2 = serializer2.save()
>>> serializer2.data
{'username': '4d46f60c84be4ae09090bb1751b9e289',
 'email': 'test@example.com',
 'first_name': 'Takayuki',
 'last_name': 'Shimizukawa',
 'full_name': 'Takayuki Shimizukawa'}
>>> u is u2  # 実体は同じ(もちろんIDも)
True

# パスワードは設定されているが write_only なので 読み出されていない
>>> u.check_password('something')
True
>>> u.password
'pbkdf2_sha256$100000$Va5TbTa8wpGP$zkyS6nDED3K19+KDjJkOfR3oC9f1w5bxxggsHBjg1pw='

>>> serializer.errors
{'non_field_errors': ['Invalid data. Expected a dictionary, but got list.']}

# さっきの続きから

class UsersSerializer(serializers.ListSerializer):
    child = UserSerializer()

    full_name = serializers.SerializerMethodField()

    def get_full_name(self, instance):
        return instance.get_full_name()  # User に元からあるメソッドを呼び出してるだけ

    class Meta:
        model = User
        fields = ('username', 'email', 'first_name', 'last_name', 'full_name')
        extra_kwargs = {
            'username': {'read_only': True},
            'password': {'write_only': True},
        }

    def create(self, validated_data):
        users = []
        for user_data in validated_data:
            password = user_data.pop('password', 'something')  # そのまま使っちゃだめだよ
            users.append(User(username=uuid.uuid4().hex, password=make_password(password), **user_data))
        return User.objects.bulk_create(users)

assert self.child is not None, '`child` is a required argument.'
AssertionError: `child` is a required argument.

assert not inspect.isclass(self.child), '`child` has not been instantiated.'
AssertionError: `child` has not been instantiated.

>>> serializer = UsersSerializer(data=[
...   {'first_name': 'Takayuki', 'last_name': 'Shimizukawa', 'username': 'test', 'email': 'test@example.com'},
...   {'first_name': 'Takanori', 'last_name': 'Suzuki', 'username': 'test', 'email': 'test2@example.com'},
... ]  # ここで child 引数に指定することもできる。引数のほうが優先。
... #, child=UserSerializer()
... )
>>> serializer.is_valid()
True
# 保存までできた
>>> sh, ta = serializer.save()
>>> sh.get_full_name()
'Takayuki Shimizukawa'
>>> ta.get_full_name()
'Takanori Suzuki'

# 発行されたクエリを見るために connection.queries を参照する
>>> from django.db import connection
>>> print(connection.queries[-1]['sql'])  # 一応バルクインサートになってますね
INSERT INTO "auth_user" ("password", "last_login", "is_superuser", "username", "first_name", "last_name", "email", "is_staff", "is_active", "date_joined")
SELECT 'pbkdf2_sha256$100000$7hAtQ2FFWVJ5$lC/SefOqFH1QzZ4ydzOz3s5ee6pMK7EQSrH0g1zyPVk=', NULL, 0, '8820a1d85233443e91c23847a9bf8928', 'Takayuki', 'Shimizukawa', 'test@example.com', 0, 1, '2018-01-23 10:38:38.718964'
UNION ALL SELECT 'pbkdf2_sha256$100000$mv7KOwcvBHyM$EjEooDwSfwiaOpEX/EQ4L33vbUjFUImTm27whpg29dQ=', NULL, 0, '825392f05208496ea05971b5869ee049', 'Takanori', 'Suzuki', 'test2@example.com', 0, 1, '2018-01-23 10:38:38.824717'

class MyCallable(object):
    def __call__(self):
        print('ここで', self.field, 'を使ってごにょごにょする')
        return 'something'

    def set_context(self, field):
        self.field = field

class SomethingSerializer(serializers.Serializer):
    a = serializers.EmailField(default=MyCallable())
    b = serializers.IntegerField(read_only=True)
    c = serializers.CharField(write_only=True, required=False)
    d = serializers.RegexField(regex='[1-9].*', required=True)
    e = serializers.DateField(source='e2')

>>> ss1 = SomethingSerializer(data={'b': 2, 'c': 3, 'd': '1', 'e': '2000-01-01'})
>>> ss1.is_valid()
ここで EmailField(default=<MyCallable object>) を使ってごにょごにょする
True
# a には デフォルト値が入る
# b は 出力専用なので無視される
# 文字列フィールド c に 数値を指定すると文字列型に矯正される
# e として受け取った値は e2 に渡っている
>>> ss1.validated_data
OrderedDict([('a', 'something'), ('c', '3'), ('d', '1'), ('e2', datetime.date(2000, 1, 1))])
# required=False の c は 省略してもOK
>>> ss2 = SomethingSerializer(data={'a': 'a@example.com',  'd': '4', 'e': '2000-01-01'})
>>> ss2.is_valid()
True
# required=False の d は 省略不可
>>> ss3 = SomethingSerializer(data={'a': 'a@example.com', 'c': '3', 'e': '2000-01-01'})
>>> ss3.is_valid()
False
>>> ss3.errors
{'d': ['This field is required.']}

# めんどくさいので Mock を使う
>>> from unittest.mock import Mock
>>> something = Mock(a='a', b='10', c='c', d='d', e='e', e2='e2')
>>> ss4 = SomethingSerializer(something)
# 数値フィールドである b は 数値に 矯正される
# c は 入力専用なので無視される
# e は e2 フィールドの値が読み出されている
>>> ss4.data
{'a': 'a', 'b': 10, 'd': 'd', 'e': 'e2'}

class ComplexionSerializer(serializers.Serializer):
    face = serializers.SerializerMethodField()
    feeling = serializers.HiddenField(default=0)

    def get_face(self, instance):
        # それぞれ 黃, 赤, 緑, 青
        return ['k', 'r', 'g', 'b'][instance.feeling]

>>> ts1 = ComplexionSerializer(data={'face': 'k', 'feeling': 2})
>>> ts1.is_valid()
True
>>> ts1.validated_data
OrderedDict([('feeling', 0)])  # 外から気分を左右されない

class Tell(object):
    def __init__(self, feeling=None):
        self.feeling = feeling

>>> tell_k = Tell(feeling=0)
>>> tell_r = Tell(feeling=1)
>>> tell_g = Tell(feeling=2)
>>> tell_b = Tell(feeling=3)
>>> ComplexionSerializer(tell_k).data
{'face': 'k'}  # 黄
>>> ComplexionSerializer(tell_r).data
{'face': 'r'}  # 赤
>>> ComplexionSerializer(tell_g).data
{'face': 'g'}  # 緑
>>> ComplexionSerializer(tell_b).data
{'face': 'b'}  # 青

from rest_framework import serializers

class PermissionSerializer(serializers.ModelSerializer):
    """デフォルト"""
    class Meta:
        fields = ('name', 'content_type', 'codename')
        model = Permission

class PermissionSerializer2(serializers.ModelSerializer):
    """StringRelatedFieldを使ってみる"""
    content_type = serializers.StringRelatedField()
    class Meta:
        fields = ('name', 'content_type', 'codename')
        model = Permission

class PermissionSerializer3(serializers.ModelSerializer):
    """PrimaryKeyRelatedFieldを使ってみる"""
    content_type = serializers.PrimaryKeyRelatedField(queryset=ContentType.objects.filter())
    class Meta:
        fields = ('name', 'content_type', 'codename')
        model = Permission

# 以下2行は以降省略
from django.contrib.auth.models import User, Permission
from django.contrib.contenttypes.models import ContentType

ct = ContentType.objects.create(app_label='test', model='auth.User')
p = Permission.objects.create(name='test permission', content_type=ct, codename='test_perm')

>>> ps = PermissionSerializer(p)
>>> ps2 = PermissionSerializer2(p)
>>> ps3 = PermissionSerializer3(p)
# プライマリキーが出力される
>>> ps.data
{'name': 'test permission', 'content_type': 12, 'codename': 'test_perm'}
# 紐づくコンテンツの __str__ or __unicode__ が出力される
>>> ps2.data
{'name': 'test permission', 'content_type': 'auth.User', 'codename': 'test_perm'}
# プライマリキー が出力される
>>> ps3.data
{'name': 'test permission', 'content_type': 12, 'codename': 'test_perm'}

>>> ps = PermissionSerializer(data={'name': 'input test1', 'content_type': 12, 'codename': 'input test1'})
>>> ps2 = PermissionSerializer2(data={'name': 'input test2', 'content_type': 12, 'codename': 'input test2'})
>>> ps3 = PermissionSerializer3(data={'name': 'input test3', 'content_type': 12, 'codename': 'input test3'})

>>> ps.is_valid()
True
>>> ps2.is_valid()
True
>>> ps3.is_valid()
True
>>> ps.save()
<Permission: test | auth.User | input test1>
>>> ps2.save()
Traceback (most recent call last):
  File "/root/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/root/venv/lib/python3.6/site-packages/django/db/backends/sqlite3/base.py", line 303, in execute
    return Database.Cursor.execute(self, query, params)
sqlite3.IntegrityError: NOT NULL constraint failed: auth_permission.content_type_id

>>> ps3.save()
<Permission: test | auth.User | input test3>

>>> ps3re = PermissionSerializer3(data={'name': 'input test3', 'content_type': ct, 'codename': 'input test3'})
>>> ps3re.is_valid()
False
>>> ps3re.errors
{'content_type': ['Incorrect type. Expected pk value, received ContentType.']}

class PermissionSerializer4(serializers.ModelSerializer):
    """PrimaryKeyRelatedFieldを使ってみる"""
    user_set = serializers.PrimaryKeyRelatedField(queryset=User.objects.filter(is_active=True), many=True)
    class Meta:
        fields = ('name', 'content_type', 'codename', 'user_set')
        read_only_field = ('content_type',)
        model = Permission

# ユーザはこの3レコード
>>> User.objects.all().values('id', 'username', 'is_active')
<QuerySet [{'id': 25, 'username': 'haru', 'is_active': False}, {'id': 26, 'username': 'shimizukawa', 'is_active': True}, {'id': 27, 'username': 'takanory', 'is_active': True}]>

>>> ps4 = PermissionSerializer4(p)
>>> ps4.data
{'name': 'test permission', 'content_type': 12, 'codename': 'test_perm', 'user_set': [25, 26, 27]}

>>> ps4 = PermissionSerializer4(data={'name': 'input test3', 'content_type': 12, 'codename': 'input test3', 'user_set': [25, 26, 27]})
>>> ps4.is_valid()
False
>>> ps4.errors
{'user_set': ['Invalid pk "25" - object does not exist.']}

>>> ps4 = PermissionSerializer4(data={'name': 'input test4', 'content_type': 12, 'codename': 'input test4', 'user_set': [26, 27]})
>>> ps4.is_valid()
True
>>> p4 = ps4.save()
>>> p4.user_set.all()
<QuerySet [<User: shimizukawa>, <User: takanory>]>

class ContentTypeSerializer(serializers.ModelSerializer):
    class Meta:
        model = ContentType
        fields = ('app_label', 'model',)


class PermissionSerializer5(serializers.ModelSerializer):
    content_type = ContentTypeSerializer()

    class Meta:
        fields = ('name', 'content_type', 'codename')
        model = Permission

>>> ps5 = PermissionSerializer5(p)
>>> ps5.data
{'name': 'test permission',
 'content_type': OrderedDict([('app_label', 'test'), ('model', 'auth.User')]),
 'codename': 'test_perm',
}

>>> ps5 = PermissionSerializer5(data={
...  'name': 'input test1',
...  'content_type': 12,
...  'codename': 'input test1'
... })
>>> ps5.is_valid()
False
>>> ps5.errors
{'content_type': {'non_field_errors': ['Invalid data. Expected a dictionary, but got int.']}}

>>> ps5 = PermissionSerializer5(data={
...  'name': 'input test1',
...  'content_type': {'app_label': 'test2', 'model': 'auth.User'},
...  'codename': 'input test1'
... })
>>> ps5.is_valid()
True
>>> p5 = ps5.save()
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/root/venv/lib/python3.6/site-packages/rest_framework/serializers.py", line 214, in save
    self.instance = self.create(validated_data)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/serializers.py", line 903, in create
    raise_errors_on_nested_writes('create', self, validated_data)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/serializers.py", line 797, in raise_errors_on_nested_writes
    class_name=serializer.__class__.__name__
AssertionError: The `.create()` method does not support writable nested fields by default.
Write an explicit `.create()` method for serializer `builtins.PermissionSerializer5`, or set `read_only=True` on nested serializer fields.

class PermissionSerializer6(serializers.ModelSerializer):
    content_type = ContentTypeSerializer(read_only=True)

    class Meta:
        fields = ('name', 'content_type', 'codename')
        model = Permission

>>> ps6 = PermissionSerializer6(p)
>>>
>>> ps6.data
{'name': 'test permission',
 'content_type': OrderedDict([('app_label', 'test'), ('model', 'auth.User')]),
 'codename': 'test_perm'}

>>> ps6 = PermissionSerializer6(data={
...  'name': 'input test1',
...  'content_type': 12,
...  'codename': 'input test1'
... })
>>> ps6.is_valid()
True
>>> p6 = ps6.save()
Traceback (most recent call last):
  File "/root/venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "/root/venv/lib/python3.6/site-packages/django/db/backends/sqlite3/base.py", line 303, in execute
    return Database.Cursor.execute(self, query, params)
sqlite3.IntegrityError: NOT NULL constraint failed: auth_permission.content_type_id

class PermissionSerializer7(serializers.ModelSerializer):
    content_type = ContentTypeSerializer(read_only=True)
    content_type_id = serializers.PrimaryKeyRelatedField(
        queryset=ContentType.objects.filter(), source='content_type', write_only=True)

    class Meta:
        fields = ('name', 'content_type', 'codename', 'content_type_id',)
        model = Permission

>>> ps7 = PermissionSerializer7(p)
>>> ps7.data
{'name': 'test permission',
 'content_type': OrderedDict([('app_label', 'test'), ('model', 'auth.User')]),
 'codename': 'test_perm'}

>>> ps7 = PermissionSerializer7(data={
...  'name': 'input test7',
...  'content_type_id': 12,
...  'codename': 'input test7'
... })
>>> ps7.is_valid()
True
>>> ps7.validated_data
OrderedDict([('name', 'input test7'), ('codename', 'input test7'), ('content_type', <ContentType: auth.User>)])
>>> p7 = ps7.save()
>>> p7
<Permission: test | auth.User | input test7>

from rest_framework import serializers

class ScoreListField(serializers.ListField):
    child = serializers.IntegerField(max_value=100)

>>> sl = ScoreListField(min_length=1, max_length=3)
>>> sl.run_validation([])
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 524, in run_validation
    self.run_validators(value)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 549, in run_validators
    raise ValidationError(errors)
rest_framework.exceptions.ValidationError: ['Ensure this field has at least 1 elements.']

>>> sl.run_validation([1, 2, 3])
[1, 2, 3]

>>> sl.run_validation([1, 2, 101])
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 523, in run_validation
    value = self.to_internal_value(data)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 1629, in to_internal_value
    return [self.child.run_validation(item) for item in data]
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 1629, in <listcomp>
    return [self.child.run_validation(item) for item in data]
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 524, in run_validation
    self.run_validators(value)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 549, in run_validators
    raise ValidationError(errors)
rest_framework.exceptions.ValidationError: ['Ensure this value is less than or equal to 100.']

>>> sl.run_validation([1, 2, 3, 4])
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 524, in run_validation
    self.run_validators(value)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 549, in run_validators
    raise ValidationError(errors)
rest_framework.exceptions.ValidationError: ['Ensure this field has no more than 3 elements.']

from rest_framework import serializers

class CommentDictField(serializers.DictField):
    child = CommentSerializer()

>>> cd = CommentDictField()
>>> cd.run_validation({
...     'a': {'email': 'a@example.com', 'content': 'aa', 'created': '2016-01-27T15:17:10.375877'},
...     'b': {'email': 'b@example.com', 'content': 'bbb', 'created': '2016-01-27T15:17:10.375877'},
... })
{'a': OrderedDict([
  ('email', 'a@example.com'), ('content', 'aa'), ('created', datetime.datetime(2016, 1, 27, 15, 17, 10, 375877, tzinfo=<UTC>))]),
 'b': OrderedDict([('email', 'b@example.com'), ('content', 'bbb'), ('created', datetime.datetime(2016, 1, 27, 15, 17, 10, 375877, tzinfo=<UTC>))])}

>>> cd.run_validation({
...     'c': {'email': 'c', 'content': 'foo bar', 'cccc': '2016-01-27T15:17:10.375877'},
... })
Traceback (most recent call last):
  File "<console>", line 2, in <module>
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 523, in run_validation
    value = self.to_internal_value(data)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 1674, in to_internal_value
    for key, value in data.items()
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 1674, in <dictcomp>
    for key, value in data.items()
  File "/root/venv/lib/python3.6/site-packages/rest_framework/serializers.py", line 435, in run_validation
    value = self.to_internal_value(data)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/serializers.py", line 478, in to_internal_value
    raise ValidationError(errors)
rest_framework.exceptions.ValidationError: {'email': ['Enter a valid email address.'], 'created': ['This field is required.']}

>>> cd.run_validation({
...     'd': {'email': 'd@example.com', 'content': 'foo bar', 'cccc': '2016-01-27'},
... })
Traceback (most recent call last):
  File "<console>", line 2, in <module>
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 523, in run_validation
    value = self.to_internal_value(data)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 1674, in to_internal_value
    for key, value in data.items()
  File "/root/venv/lib/python3.6/site-packages/rest_framework/fields.py", line 1674, in <dictcomp>
    for key, value in data.items()
  File "/root/venv/lib/python3.6/site-packages/rest_framework/serializers.py", line 435, in run_validation
    value = self.to_internal_value(data)
  File "/root/venv/lib/python3.6/site-packages/rest_framework/serializers.py", line 478, in to_internal_value
    raise ValidationError(errors)
rest_framework.exceptions.ValidationError: {'created': ['This field is required.']}

>>> j = serializers.JSONField(binary=True)
>>> j.run_validation('{"a": 1, "b": 2}')
{'a': 1, 'b': 2}

class Tree(object):
    def __init__(self, value, parent=None):
        self.value = value
        self.parent = parent

ta = Tree('a')
tb = Tree('b', ta)
tc = Tree('c', ta)
td = Tree('d', tc)
te = Tree('e', td)
tf = Tree('f', te)

class RecursiveField(serializers.Field):
    def to_representation(self, obj):
        _obj = TreeSerializer(obj).data
        if obj.parent:
            _obj['parent'] = TreeSerializer(obj.parent).data
        return _obj

class TreeSerializer(serializers.Serializer):
    parent = RecursiveField()
    value = serializers.CharField(default='test')

>>> TreeSerializer(tf).data
{
  'value': 'f', 'parent': {
    'value': 'e', 'parent': {
      'value': 'd', 'parent': {
        'value': 'c', 'parent': {
          'value': 'a', 'parent': None
        }
      }
    }
  }
}

class RecursiveField(serializers.Field):
    def to_representation(self, obj):
        return self.parent.__class__(obj, context=self.context).data

class TreeSerializer(serializers.Serializer):
    parent = RecursiveField()
    value = serializers.CharField(default='test')

>>> TreeSerializer(tf).data
{
  'value': 'f', 'parent': {
    'value': 'e', 'parent': {
      'value': 'd', 'parent': {
        'value': 'c', 'parent': {
          'value': 'a', 'parent': None
        }
      }
    }
  }
}

from rest_framework import serializers

class RecursiveField(serializers.Field):
    def to_representation(self, obj):
        return self.parent.__class__(obj, context=self.context).data

class TreeSerializer(serializers.Serializer):
    parent = RecursiveField()
    value = serializers.CharField(default='test')


class Tree(object):
    def __init__(self, value, parent=None):
        self.value = value
        self.parent = parent

ta = Tree('a')
tb = Tree('b', ta)
tc = Tree('c', tb)
ta.parent = tc

>>> TreeSerializer(tc).data
RecursionError: maximum recursion depth exceeded while calling a Python object

from rest_framework import serializers

class RecursiveField(serializers.Field):
    def to_representation(self, obj):
        parent = self.parent.__class__(obj, processed=self.parent.processed)
        if obj.value in self.parent.processed:
            return
        self.parent.processed.add(obj.value)
        return parent.data

class TreeSerializer(serializers.Serializer):
    parent = RecursiveField()
    value = serializers.CharField(default='test')

    def __init__(self, *args, **kwargs):
        processed = kwargs.pop('processed', set())
        super().__init__(*args, **kwargs)
        self.processed = processed


class Tree(object):
    def __init__(self, value, parent=None):
        self.value = value
        self.parent = parent


ta = Tree('a')
tb = Tree('b', ta)
tc = Tree('c', tb)
ta.parent = tc

>>> TreeSerializer(tc, processed=set()).data
{
  'value': 'c', 'parent': {
    'value': 'b', 'parent': {
      'value': 'a', 'parent': {
        'value': 'c', 'parent': None
      }
    }
  }
}

from django.contrib.auth.models import User
from rest_framework import serializers, validators

class UserSerializer(serializers.ModelSerializer):
    email = serializers.EmailField(validators=[validators.UniqueValidator(queryset=User.objects.all(), message='重複！')])

    class Meta:
        model = User
        fields = ('username', 'email')

>>> serializer = UserSerializer(data={'username': 'haru', 'email': 'test@example.com'})
>>> serializer.is_valid()
True
>>> serializer.save()
<User: haru>
>>> serializer2 = UserSerializer(data={'username': 'haro', 'email': 'test@example.com'})
>>> serializer2.is_valid()
False
>>> serializer2.errors
{'email': ['重複！']}