在scrapy中嵌套项数据的正确方法

Question

嵌套Item数据的正确方法是什么？

例如,我想要一个产品的输出:

{
'price': price,
'title': title,
'meta': {
    'url': url,
    'added_on': added_on
}

我有scrapy.Item:

class ProductItem(scrapy.Item):
    url = scrapy.Field(output_processor=TakeFirst())
    price = scrapy.Field(output_processor=TakeFirst())
    title = scrapy.Field(output_processor=TakeFirst())
    url = scrapy.Field(output_processor=TakeFirst())
    added_on = scrapy.Field(output_processor=TakeFirst())

现在,我这样做只是根据新的项目模板重新格式化管道中的整个项目:

class FormatedItem(scrapy.Item):
    title = scrapy.Field()
    price = scrapy.Field()
    meta = scrapy.Field()

并在管道中:

def process_item(self, item, spider):
    formated_item = FormatedItem()
    formated_item['title'] = item['title']
    formated_item['price'] = item['price']
    formated_item['meta'] = {
        'url': item['url'],
        'added_on': item['added_on']
    }
    return formated_item

这是正确的方法吗？还是有一种更直接的方法来解决这个问题而不违反框架的理念？

Answer 1

评论更新:看起来嵌套加载器是更新的方法.另一条评论表明这种方法会在序列化过程中导致错误.

解决这个问题的最佳方法是创建一个main和一个meta项目类/加载器.

from scrapy.item import Item, Field
from scrapy.contrib.loader import ItemLoader
from scrapy.contrib.loader.processor import TakeFirst


class MetaItem(Item):
    url = Field()
    added_on = Field()


class MainItem(Item):
    price = Field()
    title = Field()
    meta = Field(serializer=MetaItem)


class MainItemLoader(ItemLoader):
    default_item_class = MainItem
    default_output_processor = TakeFirst()


class MetaItemLoader(ItemLoader):
    default_item_class = MetaItem
    default_output_processor = TakeFirst()

样品用法:

from scrapy.spider import Spider
from qwerty.items import  MainItemLoader, MetaItemLoader
from scrapy.selector import Selector


class DmozSpider(Spider):
    name = "dmoz"
    allowed_domains = ["example.com"]
    start_urls = ["http://example.com"]

    def parse(self, response):
        mainloader = MainItemLoader(selector=Selector(response))
        mainloader.add_value('title', 'test')
        mainloader.add_value('price', 'price')
        mainloader.add_value('meta', self.get_meta(response))
        return mainloader.load_item()

    def get_meta(self, response):
        metaloader = MetaItemLoader(selector=Selector(response))
        metaloader.add_value('url', response.url)
        metaloader.add_value('added_on', 'now')
        return metaloader.load_item()

之后,您可以通过创建更多"子项目"轻松扩展您的项目.