我有以下的蜘蛛：

class WebSpider(scrapy.Spider):
    name = "web"
    allowed_domains = ["www.web.com"]
    start_urls = ["https://www.web.com/page/"]
    custom_settings = {
        "ITEM_PIPELINES": {
            "models.pipelines.ModelsPipeline": 1,
            "models.pipelines.MongoDBPipeline": 2,
        },
        "IMAGES_STORE": get_project_settings().get("FILES_STORE"),
    }

def parse_models(self, response):
    ...
    yield WebItem(image_urls=[img_url], images=[name], name=name, collection="web")

class WebItem(scrapy.Item):
    image_urls = scrapy.Field()
    images = scrapy.Field()
    name = scrapy.Field()
    collection = scrapy.Field()

MongoDBPipeline始终使用以下配置

"ITEM_PIPELINES": {
    "models.pipelines.ModelsPipeline": 1,
    "models.pipelines.MongoDBPipeline": 2,
}

"ITEM_PIPELINES": {
    "models.pipelines.MongoDBPipeline": 2,
}

但ModelsPipeline从不在以下任何配置中运行

"ITEM_PIPELINES": {
    "models.pipelines.ModelsPipeline": 1,
    "models.pipelines.MongoDBPipeline": 2,
}

"ITEM_PIPELINES": {
    "models.pipelines.ModelsPipeline": 1,
}

ModelsPipeline与MongoDBPipeline在同一个文件中，代码如下：

class ModelsPipeline(ImagesPipeline):

    def get_media_requests(self, item, info):
        pdb.set_trace()
        for image_url in item['image_urls']:
            yield scrapy.Request(image_url)

    def item_completed(self, results, item, info):
        pdb.set_trace()
        image_paths = [x['path'] for ok, x in results if ok]
        if not image_paths:
            raise DropItem("Item contains no images")
        adapter = ItemAdapter(item)
        adapter['image_paths'] = image_paths
        return item

但从不执行get_media_requests或item_completed
代码与doc https://docs.scrapy.org/en/latest/topics/media-pipeline.html相同
什么是错误的，什么是scrappy不运行ModelsPipeline

编辑

Scrapy版本是2.8.0
谢谢。