How do I display the indexes of a collection in MongoDB?

To display the indexes of a collection in MongoDB, use the getIndexes() method. This method returns information about all indexes defined on the specified collection, including the default _id index.

Syntax

db.collectionName.getIndexes();

Sample Data

Let's create a collection with sample documents ?

db.indexDemo.insertMany([
    { "StudentName": "Larry", "StudentAge": 21 },
    { "StudentName": "Mike", "StudentAge": 24 },
    { "StudentName": "Carol", "StudentAge": 20 }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c8f7c4f2f684a30fbdfd599"),
        ObjectId("5c8f7c552f684a30fbdfd59a"),
        ObjectId("5c8f7c5e2f684a30fbdfd59b")
    ]
}

Example 1: Default Indexes

Display indexes before creating any custom ones ?

db.indexDemo.getIndexes();

[
    {
        "v": 2,
        "key": {
            "_id": 1
        },
        "name": "_id_",
        "ns": "test.indexDemo"
    }
]

Example 2: After Creating Custom Indexes

Create a compound index and display all indexes ?

db.indexDemo.createIndex({ "StudentName": -1, "StudentAge": -1 });

{
    "createdCollectionAutomatically": false,
    "numIndexesBefore": 1,
    "numIndexesAfter": 2,
    "ok": 1
}

Now display all indexes ?

db.indexDemo.getIndexes();

[
    {
        "v": 2,
        "key": {
            "_id": 1
        },
        "name": "_id_",
        "ns": "test.indexDemo"
    },
    {
        "v": 2,
        "key": {
            "StudentName": -1,
            "StudentAge": -1
        },
        "name": "StudentName_-1_StudentAge_-1",
        "ns": "test.indexDemo"
    }
]

Key Points

• Every collection has a default _id index that cannot be dropped.
• The key field shows the indexed fields and their sort order (1 = ascending, -1 = descending).
• The name field displays the auto-generated index name based on the field names and sort order.

Conclusion

The getIndexes() method provides a complete view of all indexes on a collection, helping you understand query optimization and index management strategies.