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Indexes

Indexes make queries efficient by allowing MongoDB to find documents without scanning the entire collection. They also enable unique constraints, TTL (time-to-live) document expiry, geospatial queries, text search, and more.

See the official MongoDB documentation for a full conceptual overview.

Creating indexes​

createIndex returns the name of the created index as F[String].

Single-field index​

import cats.effect.IO
import mongo4cats.operations.Index

// Ascending index on one field
val name: IO[String] = collection.createIndex(Index.ascending("email"))

// Descending index
val name2: IO[String] = collection.createIndex(Index.descending("createdAt"))

Compound index​

Combine multiple fields into one index. The sort direction matters for sort-covered queries:

// Ascending on "category", then descending on "score"
val compound = Index.ascending("category").descending("score")
collection.createIndex(compound)

// Using combinedWith
val i1 = Index.ascending("category")
val i2 = Index.descending("score")
collection.createIndex(i1.combinedWith(i2))

Index options​

Use IndexOptions to configure additional index properties:

import mongo4cats.models.collection.IndexOptions

// Unique index — enforces no duplicate values
collection.createIndex(
  Index.ascending("email"),
  IndexOptions().unique(true)
)

// Partial index — only index documents matching a filter
import mongo4cats.operations.Filter
collection.createIndex(
  Index.ascending("score"),
  IndexOptions().partialFilterExpression(Filter.exists("score").toBson)
)

// TTL index — documents expire after the given number of seconds
collection.createIndex(
  Index.ascending("createdAt"),
  IndexOptions().expireAfter(30, java.util.concurrent.TimeUnit.DAYS)
)

// Sparse index — omit documents where the field is missing
collection.createIndex(
  Index.ascending("optionalField"),
  IndexOptions().sparse(true)
)

// Custom index name
collection.createIndex(
  Index.ascending("name").ascending("email"),
  IndexOptions().name("name_email_idx")
)

Text index (for full-text search)​

collection.createIndex(Index.text("description"))

// Then query with Filter.text
collection.find(Filter.text("functional programming")).all

Hashed index​

collection.createIndex(Index.hashed("userId"))

Geospatial index​

// 2dsphere for GeoJSON data
collection.createIndex(Index.geo2dsphere("location"))

// 2d for legacy coordinate pairs
collection.createIndex(Index.geo2d("location"))

Using the Java driver builders directly​

The standard MongoDB Java driver index builders are also accepted:

import com.mongodb.client.model.Indexes

val index = Indexes.compoundIndex(
  Indexes.ascending("field1"),
  Indexes.descending("field2")
)
collection.createIndex(index)

Listing indexes​

val indexes: IO[Iterable[Document]] = collection.listIndexes

// Typed — if the index documents map to a case class
val indexes: IO[Iterable[MyIndexInfo]] = collection.listIndexes[MyIndexInfo]

Dropping indexes​

// Drop by name
collection.dropIndex("email_1")

// Drop by index specification
collection.dropIndex(Index.ascending("email"))

// Drop all non-_id indexes
collection.dropIndexes