Transform the mongoDB data into multiple collections and restore to new server

Question

Problem:

want to replicate mongodb data across servers but also like to alter a few attributes before to restoring.

Server 1 (DB) -> Transform data of collection -> Server 2 (DB)

expectation:

Server 1

collectionA {
   _id: string
   name: string,
   priceValue: number, 
   orderId: string
}

on Server 2 should be

collectionA {
   _id: string
   price: number, // alter property name
   orderId: string
}

// create new collection
collectionB {
   _id: string // new ID
   name: string,
   orderId: string
}

Solution

I found a npm plugin (mongocopy) that does the same thing, but it is quite slow when dealing with large amounts of data.

Is there any other better solution to migrate the data? Thanks in advance :)

Answer 1

There is not much to explain really. After you export/import the database to new server, login with mongo shell and split the collection to 2:

db.collectionA.aggregate([
  {
    $project: {
      _id: 0,
      name: "$name",
      orderId: "$orderId"
    }
  },
  {
    "$out": "collectionB"
  }
]);

db.collectionA.aggregate([
  {
    $project: {
      _id: 1,
      price: "$priceValue",
      orderId: "$orderId"
    }
  },
  {
    "$out": "collectionA"
  }
]);

_id: 0 generates new ObjectId, _id: 1 preserves original value. Docs for $out parameter