How to clone a collection from one MongoDB to another on same server

问题

I'm using Mongo 3.2. I have two databases on my localhost named client1 and client2. Now client1 contains a collection named users. I want to clone this collection to client2.

I have tried:-

use client2

db.cloneCollection('localhost:27017', 'client1.users', { 'active' : true } )

This outputs

{ "ok" : 0.0, "errmsg" : "can't cloneCollection from self" }

Is cloning a collection from one db to another on the same server prohibited?

回答1:

Few things :

1. In general cloneCollection is used for different mongo instances but not to copy on same instances.
2. Also if you're using v4.2 you should stop using copyDB & cloneCollection cause they're deprecated compatibility-with-v4.2 & start using mongodump and mongorestore or mongoexport & mongoimport.

3. I would suggest to use mongodump & mongorestore :

   1. Cause mongodump would preserve MongoDB's data types i.e.; bson types.
   2. mongodump creates a binary where as mongoexport would convert bson to json & again mongoimport will convert json to bson while writing, which is why they're slow. You can use mongoexport & mongoimport when you wanted to analyze your collections data visually or use json data for any other purpose.

4. You can run below script in shell

   declare - a collections = ("collectionName1" "collectionName2")
   for i in "${collections[@]}"
   do
   echo "$i"
       mongodump --host "All-shards" --username=uname --password password --ssl --authenticationDatabase admin --db dbname --collection "$i"
   
       mongorestore --host=host-shard-name --port=27017 --username=uname --password=psswrd --ssl --authenticationDatabase=admin --db=dbname --collection= "$i" ./dump/dbName/"$i".bson;
   done
   

To use mongodump, you must run mongodump against a running mongod or mongos instance. So these commands are being run expecting mongo is properly installed & path setup is good, if not you can navigate to mongo folder & run like ./mongodump & ./mongorestore. Above script will be useful if you wanted to backup multiple collections, You need specify few things in script like :

1. mongodump--host "All-shards" -> Here you need to specify all shards if your MongoDB is a replica set, if not you can specify localhost:27017.

2. mongorestore --host=host-shard-name -> You've to specify one shard of replica set, else your localhost, Few things here can be optional --ssl, --username, --password.

3. So mongodump will create a folder named dump for first time which will have the sub-folders with dbNames & each sub-folder will has bson files respective to their collection names dumped, So you need to refer dbName in restore command & collection name will be taken from variable i -> ./dump/dbName/"$i".bson

Note : MongoDB v3.2 is so old & in cloud based MongoDB service Mongo-atlas it has already reached it's end of lifecycle, So please upgrade asap. If you're looking for a free mongo instance or starting with MongoDB - you can try atlas.

回答2:

db.cloneCollection() copies data directly between MongoDB instances.

https://docs.mongodb.com/v3.2/reference/method/db.cloneCollection/

That means you cannot clone inside the same mongod instance. Use mongoexport and mongoimport to clone your collection.

---

Since 4.2 MongoDb introduces $merge operator which allows copy from db1.collection to db2.collection.

来源：https://stackoverflow.com/questions/60133931/how-to-clone-a-collection-from-one-mongodb-to-another-on-same-server