如何使用pymongo从MongoDB复制一个集合并将其粘贴到另一个空集合?

问题描述

1. 我要复制完整的收藏集(例如，名称"home").
2. 然后在"home"集合中进行一些更改或删除其中的文档(不是集合).
3. 然后将已更改的"home"集合从项目1替换为其默认状态.

我下一步:

db = client["database"]
home = db['home'].find()  # get collection.
db['home'].remove({})  # remove doc from home
for i in home:
      self.db['home'].insert(i)

但是集合为空.

推荐答案

您的代码示例的问题是find()返回数据库游标到集合，而不是集合中的所有文档.因此，当您remove来自home集合的所有文档时，光标也将指向一个空集合.

The problem with your code example is that find() returns a database cursor to the collection, not all documents in the collection. So when you remove all documents from the home collection, the cursor will also point to an empty collection.

为了将一个集合复制到同一服务器中的另一个集合，您可以利用 MongoDB聚合运算符 $ match 和 $ out

In order to copy a collection to another collection in the same server, you can utilise MongoDB Aggregation operator $match and $out

pipeline = [ {"$match": {}},
             {"$out": "destination_collection"},
]
db.source_collection.aggregate(pipeline)

使用示例代码，立即，您可以执行

Using your example code, now you can do

source = db["source_collection"]
destination = db["destination_collection"]

# Remove all documents, or make modifications.
source.remove({})

# Restore documents from the source collection.
for doc in destination:
      source.insert(doc)
# or instead you can just use the same aggregation method above but reverse the collection name.

注意: db.从MongoDB v3.0开始，不推荐使用collection.copyTo().

如果您想复制到另一台MongoDB服务器，则可以使用 db.cloneCollection().在PyMongo中，它将是以下命令:

If you would like to copy to another MongoDB server, you can utilise db.cloneCollection(). In PyMongo it would be a command such below:

db.command("cloneCollection", **{'collection': "databaseName.source_collection", 'from': "another_host:another_port"})

根据您的总体目标，您可能会发现 MongoDB备份方法有用.

Depending on your overall goal, you may find MongoDB BackUp methods useful.

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