如何在使用Scrapy时向数据库中插入多个项目？

# settings.py

ITEM_PIPELINES = {
    'myproject.pipelines.MyPipeline': 300,
}

DB_SETTINGS = {
    'db_type': 'mysql',
    'host': 'localhost',
    'port': 3306,
    'db_name': 'mydatabase',
    'username': 'myuser',
    'password': 'mypassword',
}

# pipelines.py

import pymysql

class MyPipeline(object):
    def __init__(self):
        self.db_settings = settings.get('DB_SETTINGS')

    def open_spider(self, spider):
        self.conn = pymysql.connect(
            host=self.db_settings['host'],
            port=self.db_settings['port'],
            user=self.db_settings['username'],
            password=self.db_settings['password'],
            db=self.db_settings['db_name'],
            charset='utf8mb4',
            cursorclass=pymysql.cursors.DictCursor
        )
        self.cursor = self.conn.cursor()

    def close_spider(self, spider):
        self.conn.close()

    def process_item(self, item, spider):
        # 处理item并插入数据库
        sql = "INSERT INTO mytable (field1, field2) VALUES (%s, %s)"
        self.cursor.execute(sql, (item['field1'], item['field2']))
        self.conn.commit()
        return item

# spider.py

import scrapy
from myproject.items import MyItem

class MySpider(scrapy.Spider):
    name = 'myspider'
    start_urls = ['http://www.example.com']

    def parse(self, response):
        # 解析网页并提取数据
        item = MyItem()
        item['field1'] = response.css('selector1').get()
        item['field2'] = response.css('selector2').get()
        yield item