我在从两个模型之间的多对多关系返回数据时遇到了问题。我不想显示所有 货币？基于 created_at` 字段，具有与该货币相关的最新Ticker对象的对象。我想知道如何在 json 中创建这样的输出？
期望的输出
[
{
"id": 1,
"name": "Bitcoin",
"symbol": "BTC",
"img": "/media/static/img/currencies/bitcoin_uzSOQkH.png",
"tickers":
{
"rank": 1,
"price_dkk": "111239.222648",
"market_cap_dkk": 1861795518438,
"percent_change_1h": "0.03",
"percent_change_24h": "2.44",
"percent_change_7d": "46.80",
"created_at": "2017-12-12T20:11:49.995851Z"
}
}
]
查看
class CurrencyGetView(ProtectedResourceView):
def get(self, request):
currencies = CurrencySerializer(Currency.objects.all(), many=True)
return JsonResponse(currencies.data, safe=False)
序列化器
class TickerSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = Ticker
fields = ('rank', 'price_dkk', 'market_cap_dkk', 'percent_change_1h', 'percent_change_24h', 'percent_change_7d', 'created_at', )
class CurrencySerializer(serializers.HyperlinkedModelSerializer):
tickers = TickerSerializer(many=True)
class Meta:
model = Currency
fields = ('id', 'name','symbol', 'img', 'tickers',)
模型
class Ticker(models.Model):
rank = models.IntegerField()
price_dkk = models.DecimalField(max_digits=20, decimal_places=6)
market_cap_dkk = models.BigIntegerField()
percent_change_1h = models.DecimalField(max_digits=4, decimal_places=2)
percent_change_24h = models.DecimalField(max_digits=4, decimal_places=2)
percent_change_7d = models.DecimalField(max_digits=4, decimal_places=2)
created_at = models.DateTimeField(auto_now_add=True)
class Meta:
verbose_name_plural = _('Ticker')
def __str__(self):
return self.id
class Currency(models.Model):
symbol = models.CharField(max_length=4, default='BTC', unique=True)
name = models.CharField(max_length=20, default='Bitcoin', unique=True)
img = models.ImageField(upload_to = 'static/img/currencies', blank=True)
is_active = models.BooleanField(default=False)
tickers = models.ManyToManyField(Ticker)
class Meta:
verbose_name_plural = 'currencies'
def __str__(self):
return self.name
最佳答案
我觉得这应该在查询级别解决，最好使用 prefetch_related。但是Django can't slice Prefetch objects .无赖。和 Subquery非常缓慢。
我能想到的最佳解决方案是创建一个 SerializerMethodField ，它使用切片数据集调用 TickerSerializer。缺点是 DRF 将为列表中的每个 Currency 对象触发额外的 SQL 查询。
from rest_framework.fields import SerializerMethodField
class CurrencySerializer(serializers.HyperlinkedModelSerializer):
ticker = SerializerMethodField()
def get_ticker(self, obj):
return TickerSerializer(
instance=obj.tickers.order_by('-created_at')[:1],
many=True
).data
class Meta:
model = Currency
fields = ('id', 'name','symbol', 'img', 'tickers', 'ticker')
关于python - 显示嵌套关系的最后一个对象，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47839606/