这次就是由于一个问题，引出了一系列的思路

问题是：scrapy爬取的数据控制台已经有内容输出，但是数据库中没有？
下面是我过程中的问题：其实大多数的代码问题都是由于自己代码不熟练造成的

圈出来的内容在编写中是不能随意改变得（三种数据库的pipelines的写法结构相同）。
解答：我的错误就是由于将process_item ,顺手错写成了process_spider，导致数据无法放入数据库，而且各种求教，解决都不行，最后检查代码才发现

下方是完整正确的代码

项目包结构：

items.py

import scrapy
class QidianHotItem(scrapy.Item):
    # define the fields for your item here like:
    name = scrapy.Field()#书名
    author = scrapy.Field()#作者
    type = scrapy.Field()#类型
    status=scrapy.Field()#小说目前的状态（连载或完结）
    info = scrapy.Field()#小说简介
    up_date = scrapy.Field()#最近更新

qidian_hot_spider.py

#coding:utf-8
#爬取起点中文网的小说信息

from scrapy import Request
from scrapy.spiders import Spider
from qidian_hot.items import QidianHotItem 
from scrapy.loader import ItemLoader
class HotSaleSpider(Spider):
    name="hot"#爬虫名称
    
    #伪装浏览器
    def start_requests(self):
        url="https://www.qidian.com/rank/hotsales?style=1&page=1"
        self.current_page=1
        yield Request(url)
        #Request(url, callback, method, headers, body, cookies, meta, encoding, priority, dont_filter, errback, flags)
    def parse(self, response):  #数据解析
        list_selector = response.xpath("//div[@class='book-mid-info']")
        
        #使用xpath定位
        for one_selector in list_selector:
            #获取小说信息
            name=one_selector.xpath("h4/a/text()").extract()[0]
                   
            #小说作者
            author=one_selector.xpath("p[1]/a[1]/text()").extract()[0]
              
            #小说类型
            type=one_selector.xpath("p[1]/a[2]/text()").extract()[0]
              
            #状态
            status=one_selector.xpath("p[1]/span/text()").extract()[0]
              
            #小说简介
            info=one_selector.xpath("p[2]/text()").extract()[0]
             
            #更新
            up_date = one_selector.xpath("p[3]/a/text()").extract()[0]
             
            #使用items
            item = QidianHotItem()
            item["name"] = name
            item["author"]=author
            item["type"]=type
            item["status"]=status
            item["info"]=info
            item["up_date"]=up_date
            yield item
            #获取下一页的数据
            self.current_page+=1
            if self.current_page<=2:
                next_url="https://www.qidian.com/rank/hotsales?style=1&page=%d"%self.current_page
                yield Request(next_url)

settings.py

USER_AGENT ="Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36"
ROBOTSTXT_OBEY = False  #不遵守robots.txt 规则
#初始状态是默认关闭的      300代表的是先后顺序，在多个管道的时候
ITEM_PIPELINES = {
    'qidian_hot.pipelines.QidianHotPipeline': 300,
#     'qidian_hot.pipelines.MongoDB_Spider': 400, #这是MongoDB数据库的管道
    'qidian_hot.pipelines.Redis_Spider': 400,  #这是redis数据库的管道
#     'qidian_hot.pipelines.MySQLPipeline': 500,  #这是mysql数据库
}

三种数据库的配置项,书写在settings.py文件中

#数据库  MySQL
MYSQL_DB_NAME = "hot_qidian"
MYSQL_HOST = "localhost"
MYSQL_USER = "root"
MYSQL_PASSWORD = "123456"
#数据库MongoDB
MONGODB_HOST = "127.0.0.1"
MONGODB_PORT = 27017
MONGODB_NAME = "qidian"
MONGODB_COLLECTION = "hot"       
#Redis 数据库
REDIS_HOST = "127.0.0.1"
REDIS_PORT = 6379
REDIS_DB_INDEX = 1

1、使用MySQL数据库

class MySQLPipeline(object):
    #在spider开始之前，调用一次
    def open_spider(self,spider):
        db_name = spider.settings.get("MYSQL_DB_NAME","hot_qidian")
        host = spider.settings.get("MYSQL_HOST","localhost")
        user = spider.settings.get("MYSLQ_USER","root")
        password = spider.settings.get("MYDSQL_PASSWORD","123456")
      #连接数据库
        self.db_conn = MySQLdb.connect(db = db_name,
                                       host = host,
                                       user = user,
                                       password = password,
                                       charset = "utf8"
                                        )
        self.db_cursor = self.db_conn.cursor()  #得到游标
      
    #处理每一个item
    def process_item(self,item,spider):
        values = (item["name"],item["author"],item["type"],item["status"],item["up_date"])
        #确定sql语句
        sql = 'insert into hot(name,author,type,status,up_date) values(%s,%s,%s,%s,%s)'
        self.db_cursor.execute(sql,values)
        return item
      
    #在spider结束时，调用一次
    def close_spider(self,spider):
        self.db_conn.commit()  #提交数据 
        self.db_cursor.close()
        self.db_conn.close()

一次使用成功。
2、MongoDB数据库

import pymongo     
class MongoDB_Spider(object):
    #开始之前调用一次
    def open_sipder(self,spider):
        host = spider.settings.get('MONGODB_HOST')
        port = spider.settings.get('MONGODB_PORT')
        db_name = spider.settings.get('MONGODB_NAME')
        db_collection = spider.settings.get('MONGODB_COLLECTION')
        self.db_client = pymongo.MongoClient(host=host,port = port)
        #指定数据库
        self.db_name = self.db_client[db_name]
        #指定集合,得到一个集合对象
        self.db_collection = self.db_name[db_collection]
             
    #处理每一个item数据
    def process_item(self,item,spider):
        item_hot = dict(item)
        self.db_collection.insert(item_hot)
    #结束时，调用一次
    def close_spider(self,spider):
        self.db_client.close()

3、连接redis数据库

import redis
class Redis_Spider(object):
    num = 1
    def __init__(self):
        self.item_set=set()
    def open_spider(self,spider):
        host = spider.settings.get("REDIS_HOST","localhost")
        port = spider.settings.get("REDIS_PORT",6379)
        db_index = spider.settings.get("REDIS_DB_INDEX",1)
        self.db_conn = redis.Redis(host=host,port=port,password='',db=db_index)
        #将数据存储到数据库中
    def process_item(self,item,spider):
        print(self.db_conn)
        try:
            item_dict = dict(item)
            self.db_conn.rpush("novel",item_dict)
            return item
        except Exception as ex:
            print(ex)
    def close_spider(self,spider):#关闭
        self.db_conn.connection_pool.disconnect()
      

上面的代码运行是无错的