如何在替换整个文档时更新mongodb文档？

import pymongo

# 连接到新的MongoDB实例
new_db = pymongo.MongoClient("mongodb://new_host:new_port/new_database")

# 连接到旧的MongoDB实例
old_db = pymongo.MongoClient("mongodb://old_host:old_port/old_database")

# 导入旧数据库的集合
old_collections = old_db["collection_name"]

# 导出旧文档
old_docs = old_collections.find()

# 创建新文档实例
new_docs = []

# 遍历旧文档并更新
for old_doc in old_docs:
    # 根据条件筛选和更新新文档
    new_doc = {
        "id": old_doc["_id"],
        "field_to_update": "new_value"
    }
    new_docs.append(new_doc)

# 保存新文档
new_collections = new_db["collection_name"]
new_collections.insert_many(new_docs)

# 删除旧文档
old_collections.remove_many({"_id": {"$in": old_docs.map(lambda doc: doc["_id"])}})