MongoDB How to copy index definitions from one collection to another?

Question

I know there's a way to do db.collection.getIndexes() Which will list all the indexes defined for a collection. Is there a way to copy and create those index definitions to another collection?

There's a lot of them and I don't want to do them one by one.

regarding the duplicated question comment: I do not wish to copy a collection. I wish to export indexes in a format that I can apply to another collection.

Answer 1

To do this directly in MongoDB do the following,

The following command will generate mongo DB queries for existing indexes of all collections,

db.getCollectionNames().forEach(function(col) {
    var indexes = db[col].getIndexes();
    indexes.forEach(function (c) {
        var fields = '', result = '', options = {};
        for (var i in c) {
            if (i == 'key') {
                fields = c[i];
            } else if (i == 'name' && c[i] == '_id_') {
                return;
            } else if (i != 'name' && i != 'v' && i != 'ns') {
                options[i] = c[i];
            }
        }
        var fields = JSON.stringify(fields);
        var options = JSON.stringify(options);
        if (options == '{}') {
            result = "db." + col + ".createIndex(" + fields + "); ";
        } else {
            result = "db." + col + ".createIndex(" + fields + ", " + options + "); ";
        }
        result = result
            .replace(/{"floatApprox":-1,"top":-1,"bottom":-1}/ig, '-1')
            .replace(/{"floatApprox":(-?\d+)}/ig, '$1')
            .replace(/\{"\$numberLong":"(-?\d+)"\}/ig, '$1');
        print(result);
    });
});

The above command will output something like the following, based on the amount of collection you have

db.User.createIndex({"createdAt":-1}, {"background":true}); 

db.User.createIndex({"updatedAt":-1}, {"background":true}); 

db.Login.createIndex({"loginDate":-1}, {"background":true}); 

So after executing this, copy the MongoDB queries that are generated above to create the indexes to the new collection, Change the collection name in that then execute it.

For eg: to copy all indexes belonging to the User collection to the UserNew collection, I will rename the query's old collection name to new like the following and execute it, that is it, now you have all the indexes copied to a new collection from the old one.

db.UserNew.createIndex({"createdAt":-1}, {"background":true}); 

db.UserNew.createIndex({"updatedAt":-1}, {"background":true}); 

Credits: http://aleksandrmaiorov.com/2019/04/29/mongo-how-to-copy-indexes-from-one-database-to-another/

Answer 2

For example I have one existing user collection with indexes _id_, name_1, email_1 and website_1

Then I have another collection called usertest, I want to copy indexes from user collection to usertest collection. The following commands works for this scenario:

1. Copy both index key and index options

   var indexes = db.user.getIndexes();
   
   indexes.forEach(function(index){
       delete index.v;
       delete index.ns;
       var key = index.key;
       delete index.key
       var options = [];
       for (var option in index) {
           options.push(index[option]);
       }
      db.usertest.createIndex(key, options);
   });
   

2. Copy index key only (batch processing)

   var indexKeys = db.user.getIndexKeys();
   db.usertest.createIndexes(indexKeys);
   

Hope this will be helpful. Here's the doc: createIndexes