[mongodb] How to copy a collection from one database to another in MongoDB

There are different ways to do the collection copy. Note the copy can happen in the same database, different database, sharded database or mongod instances. Some of the tools can be efficient for large sized collection copying.

Aggregation with $merge: Writes the results of the aggregation pipeline to a specified collection. Note that the copy can happen across databases, even the sharded collections. Creates a new one or replaces an existing collection. New in version 4.2. Example: db.test.aggregate([ { $merge: { db: "newdb", coll: "newcoll" }} ])

Aggregation with $out: Writes the results of the aggregation pipeline to a specified collection. Note that the copy can happen within the same database only. Creates a new one or replaces an existing collection. Example: db.test.aggregate([ { $out: "newcoll" } ])

mongoexport and mongoimport: These are command-line tools. mongoexport produces a JSON or CSV export of collection data. The output from the export is used as the source for the destination collection using the mongoimport.

mongodump and mongorestore: These are command-line tools. mongodump utility is for creating a binary export of the contents of a database or a collection. The mongorestore program loads data from a binary database dump created by mongodump into the destination.

db.cloneCollection(): Copies a collection from a remote mongod instance to the current mongod instance. Deprecated since version 4.2.

db.collection.copyTo(): Copies all documents from collection into new a Collection (within the same database). Deprecated since version 3.0. Starting in version 4.2, MongoDB this command is not valid.

NOTE: Unless said the above commands run from mongo shell.

Reference: The MongoDB Manual.

You can also use a favorite programming language (e.g., Java) or environment (e.g., NodeJS) using appropriate driver software to write a program to perform the copy - this might involve using find and insert operations or another method. This find-insert can be performed from the mongo shell too.

You can also do the collection copy using GUI programs like MongoDB Compass.