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Duplicate a collection in the same database is an amazing task. It saves time and effort. This tutorial demonstrates how to replicate a collection in the same database using MongoDB mongodump, mongorestore, aggregate()and .forEach()

Copying collections in the same database when working in MongoDB

In older versions of MongoDB, like less than 3.0, we could use copyTo()method as to db.collection_name.copyTo()copy a collection, but it is deprecated now.

evalIt is also deprecated starting with MongoDB version 4.2. Note that db.collection_name.copyTo()it is wrapped eval, which means we cannot use any of them to copy collections if we have MongoDB 4.2 or higher.

There are other ways to replicate collections in the same database in newer versions of MongoDB. Some of them are listed here.

Let’s start learning them one by one.

To replicate a collection in the same database in MongoDB mongodump, usemongorestore

This is the quickest way to clone/duplicate a collection in the same database using the MongoDB Database Tools; specifically, we can use mongodumpand mongorestore. The Database Tools are a suite of command-line utilities for working in MongoDB.

We can use the following command in the Windows command prompt to check the versions of mongodumpand mongorestore. If it successfully returns the corresponding version, the database tools are installed.

Otherwise, follow this to install the database tools.

Sample code:

C:/Users/Dell> mongodump --version

Sample code:

C:/Users/Dell> mongorestore --version

Remember, we have to execute the mongodumpand mongorestorecommands from the command line of the system, for example, from the command prompt in Windows OS or terminal if we are using Ubuntu. Never run this command from the mongo shell.

Once we have the database tools for MongoDB, run the following command to teachersdump the collection into the same database: 'test`.

Sample code:

C:/Users/Dell> mongodump -d test -c teachers

Output:

2022-05-27T13:05:14.497+0500    writing test.teachers to dump\test\teachers.bson
2022-05-27T13:05:14.503+0500    done dumping test.teachers (3 documents)

The above output indicates that the dump file is written dump\test\teachers.bson. So, we need to restore it using the command given below.

Sample code:

C:/Users/Dell>mongorestore -d test -c teachers1 --dir=dump/<db>/<sourcecollection.bson>

Output:

2022-05-27T13:05:28.085+0500    checking for collection data in dump\test\teachers.bson
2022-05-27T13:05:28.088+0500    reading metadata for test.teachers1 from dump\test\teachers.metadata.json
2022-05-27T13:05:28.252+0500    restoring test.teachers1 from dump\test\teachers.bson
2022-05-27T13:05:28.312+0500    finished restoring test.teachers1 (3 documents, 0 failures)
2022-05-27T13:05:28.312+0500    no indexes to restore for collection test.teachers1
2022-05-27T13:05:28.313+0500    3 document(s) restored successfully. 0 document(s) failed to restore.

The output will be as shown above, which means the collection has been copied successfully. If the target collection named does not exist in the current database teachers1, it will be created.

Next, open the mongo shell and execute the following query to see if the replicated collection exists.

Sample code:

> show collections

Output:

teachers
teachers1

Alternatively, we can also export a collection from mongoexporta database using and then import it into a collection in the same database using .testteachersmongoimportteachers2

Sample code:

C:/Users/Dell> mongoexport -d test -c teachers | mongoimport -d test -c teachers2 --drop

aggregate()To copy a collection in the same database in MongoDB, use the

Sample code:

> db.teachers.aggregate([{$out: "teachers3"}])

This command is executed using the mongo shell. Afterwards, we use show collectionsthe command to see teachers3if the exists.

Sample code:

> show collections

Output:

teachers
teachers1
teachers2
teachers3

We are using aggregation pipeline to return data from teacherscollection and write them to the specified collection, here teachers3. We can use this approach if we have MongoDB 4.4 or higher.

Use forEach()loop to copy collections in the same database in MongoDB

Sample code:

> db.teachers.find().forEach((doc) => {
    db.teachers4.insert(doc)
  })

Use the following query to confirm teachers4that ​​is in the same database.

Sample code:

> show collections

Output:

teachers
teachers1
teachers2
teachers3
teachers4

This method is the slowest compared to all the above methods due to the use of loop. It iterates over all the documents of the source collection and inserts them one by one into the target collection.