Advanced Indexing

Beyond simple single-field and compound indexes, MongoDB offers specialized index types for specific data structures and use cases.

1. Multikey Indexes

If you index a field that contains an array, MongoDB automatically creates a Multikey Index. This allows you to query specific elements within the array efficiently.

// Indexing a "tags" array
db.products.createIndex({ tags: 1 })

2. Hashed Indexes

Hashed indexes maintain entries with hashes of the values of the indexed field. These are primarily used for Hashed Sharding to ensure even distribution of data across a cluster.

db.users.createIndex({ user_id: "hashed" })

3. Wildcard Indexes

Wildcard indexes support queries against unknown or arbitrary fields. This is perfect for collections with highly dynamic schemas.

db.products.createIndex({ "metadata.$**": 1 })

4. Partial Indexes

Matches only those documents that meet a specified filter expression. This saves space and improves write performance for sparse data.

// Only index documents where rating is greater than 5
db.restaurants.createIndex(
  { cuisine: 1, name: 1 },
  { partialFilterExpression: { rating: { $gt: 5 } } }
)