python中mongodb查询指定字段值是否存在的方法：
import pymongo
# 链接数据库
client = pymongo.MongoClient(host='127.0.0.1', port=27017)
# 数据库登录需要帐号密码的话
client.runoob.authenticate('runoob', 'runoob',mechanism='SCRAM-SHA-1')
db = client['runoob'] # 获得数据库的句柄
coll = db['details'] # 获得collection的句柄
# python中mongodb判断某字段的值是否存在
count = coll.count_documents({ "articleid": "d5a603693d943e77be0c9901a92cce28" })
if count !=0:
print("有")
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