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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?
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A unique index ensures that the indexed fields do not store duplicate values; i.e. enforces uniqueness for the indexed fields. By default, MongoDB creates a unique index on the _id field during the creation of a collection.
To get unique values and ignore duplicates, use distinct() in MongoDB. The distinct() finds the distinct values for a specified field across a single collection and returns the results in an array.
You can find all the available indexes in a MongoDB collection by using the getIndexes method. This will return all the indexes in a specific collection. Result: The output contains the default _id index and the user-created index student name index.
Use the db. collection. explain() or the cursor. explain() method in executionStats mode to return statistics about the query process, including the index used, the number of documents scanned, and the time the query takes to process in milliseconds.
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
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db.<my_collection>.getIndexes()
If some of those indexes are unique, you will see a key named "unique" with the value true.
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