Django Rest Framework 3 - 有许多额外的字段

Question

我对Django Rest Framework上的序列化程序有疑问......首先我的模型是：

class Transaction(Model):
type_choices = (
    (1, 'deposit'),
    (2, 'withdrawal')
)

status_choices = (
    (1, 'pending'),
    (2, 'made'),
    (3, 'canceled'),
    (4, 'completed')
)

name = CharField(null=True, blank=True,max_length=50,)
description = TextField(null=True, blank=True)
amount = FloatField()
type = IntegerField(choices=type_choices, )
status = IntegerField(choices=status_choices, )

client = ForeignKey(User, related_name='transaction_client', blank=True, null=True)

cards = ManyToManyField(Card, through='TransactionCard')

created_by = ForeignKey(User, related_name='transaction_created_by')
created_at = DateTimeField(auto_now_add=True, editable=False)
updated_by = ForeignKey(User, null=True, related_name='transaction_updated_by')
updated_at = DateTimeField(auto_now=True, editable=False)

class Meta:
    ordering = ('-created_at',)

def __str__(self):
    return self.name


class TransactionCard(Model):

transaction = ForeignKey(Transaction, related_name='transactioncard_transaction')
card = ForeignKey(Card, related_name='transactioncard_card')
amount = FloatField()

class Card(Model):
name = CharField(null=True, blank=True, max_length=100,)
description = TextField(null=True, blank=True,)
card_number = TextField(max_length=16, )
month_exp = IntegerField()
year_exp = IntegerField()
month_acq = IntegerField(null=True, blank=True,)
year_acq = IntegerField(null=True, blank=True, )

card_type = ForeignKey(CardType, related_name='cards_card_type')
provider = ForeignKey(Provider, related_name='cards_provider')

balance = FloatField()

active = BooleanField()

created_by = ForeignKey(User, related_name='cards_created_by')
created_at = DateTimeField(auto_now_add=True, editable=False)
updated_by = ForeignKey(User, null=True, related_name='cards_updated_by')
updated_at = DateTimeField(auto_now=True, editable=False)

class Meta:
    ordering = ('month_exp', 'year_exp',)

def __str__(self):
    return self.name

我的序列化器是：

class TransactionCreateSerializer(ModelSerializer):
created_by = StringRelatedField()
updated_by = StringRelatedField()

class Meta:
    model = Transaction
    fields = [
        'id',
        'name',
        'description',
        'amount',
        'type',
        'status',
        'client',
        'cards',
        'created_by',
        'created_at',
        'updated_by',
        'updated_at'
    ]
    extra_kwargs = {
        'created_by': {
            'read_only': True
        },
        'updated_by': {
            'read_only': True
        }
    }

def create(self, validated_data):
    pprint(validated_data.pop('cards'))
    transaction = Transaction.objects.create(**validated_data)
    return transaction

我的问题是，当我尝试将validated_data.pop（卡片）设置为错误时，我不知道为什么会这样做。

更新

它的错误：

pprint(validated_data.pop('cards))
KeyError: 'cards'