How to test if an index is unique in Mongo on the command line

Question

I'm working with a collection that someone else created, and I need to find out whether an index is unique. Is there anyway to do this from the mongo shell?

Answer 1

You can search for indexes with:

db.system.indexes.find();

To search for a unique index:

db.system.indexes.find({"unique": true});

With that, you can also add more search parameters to find specific indexes by namespace, key, etc.

Edit: Relevant documentation: http://www.mongodb.org/display/DOCS/Index-Related+Commands

Answer 2

db.<my_collection>.getIndexes()

If some of those indexes are unique, you will see a key named "unique" with the value true.