correct way to nest Item data in scrapy

Question

What is the correct way to nest Item data?

For example, I want the output of a product:

{
\'price\': price,
\'title\': title,
\'meta\': {
    \'url\'         


        

Answer 1

UPDATE from comments: Looks like nested loaders is the updated approach. Another comment suggests this approach will cause errors during serialization.

Best way to approach this is by creating a main and a meta item class/loader.

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()

Sample usage:

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()

After that, you can easily expand your items in the future by creating more "sub-items."