Index and Collection Management

MongoTemplate and ReactiveMongoTemplate provide methods for managing indexes and collections. These methods are collected into a helper interface called IndexOperations respectively ReactiveIndexOperations. You can access these operations by calling the indexOps method and passing in either the collection name or the java.lang.Class of your entity (the collection name is derived from the .class, either by name or from annotation metadata).

The following listing shows the IndexOperations interface:

Imperative
Reactive

public interface IndexOperations {

    String ensureIndex(IndexDefinition indexDefinition);

    void alterIndex(String name, IndexOptions options);

    void dropIndex(String name);

    void dropAllIndexes();

    List<IndexInfo> getIndexInfo();
}

public interface ReactiveIndexOperations {

    Mono<String> ensureIndex(IndexDefinition indexDefinition);

    Mono<Void> alterIndex(String name, IndexOptions options);

    Mono<Void> dropIndex(String name);

    Mono<Void> dropAllIndexes();

    Flux<IndexInfo> getIndexInfo();

Methods for Creating an Index

You can create an index on a collection to improve query performance by using the MongoTemplate class, as the following example shows:

Imperative
Reactive

template.indexOps(Person.class)
    .ensureIndex(new Index().on("name",Order.ASCENDING));

Mono<String> createIndex = template.indexOps(Person.class)
    .ensureIndex(new Index().on("name",Order.ASCENDING));

ensureIndex makes sure that an index for the provided IndexDefinition exists for the collection.

You can create standard, geospatial, and text indexes by using the IndexDefinition, GeoSpatialIndex and TextIndexDefinition classes. For example, given the Venue class defined in a previous section, you could declare a geospatial query, as the following example shows:

template.indexOps(Venue.class)
    .ensureIndex(new GeospatialIndex("location"));

Index and GeospatialIndex support configuration of collations.

Accessing Index Information

The IndexOperations interface has the getIndexInfo method that returns a list of IndexInfo objects. This list contains all the indexes defined on the collection. The following example defines an index on the Person class that has an age property:

Imperative
Reactive

template.indexOps(Person.class)
    .ensureIndex(new Index().on("age", Order.DESCENDING).unique());

List<IndexInfo> indexInfoList = template.indexOps(Person.class)
   .getIndexInfo();

Mono<String> ageIndex = template.indexOps(Person.class)
    .ensureIndex(new Index().on("age", Order.DESCENDING).unique());

Flux<IndexInfo> indexInfo = ageIndex.then(template.indexOps(Person.class)
   .getIndexInfo());

Methods for Working with a Collection

The following example shows how to create a collection:

Imperative
Reactive

MongoCollection<Document> collection = null;
if (!template.getCollectionNames().contains("MyNewCollection")) {
    collection = mongoTemplate.createCollection("MyNewCollection");
}

MongoCollection<Document> collection = template.getCollectionNames().collectList()
    .flatMap(collectionNames -> {
        if(!collectionNames.contains("MyNewCollection")) {
            return template.createCollection("MyNewCollection");
        }
        return template.getMongoDatabase().map(db -> db.getCollection("MyNewCollection"));
    });

Collection creation allows customization with CollectionOptions and supports collations.

Methods to interact with MongoCollections

getCollectionNames: Returns a set of collection names.
collectionExists: Checks to see if a collection with a given name exists.
createCollection: Creates an uncapped collection.
dropCollection: Drops the collection.
getCollection: Gets a collection by name, creating it if it does not exist.

Time Series

MongoDB 5.0 introduced Time Series collections that are optimized to efficiently store documents over time such as measurements or events. Those collections need to be created as such before inserting any data. Collections can be created by either running the createCollection command, defining time series collection options or extracting options from a @TimeSeries annotation as shown in the examples below.

Example 1. Create a Time Series Collection

Create a Time Series via the MongoDB Driver

template.execute(db -> {

    com.mongodb.client.model.CreateCollectionOptions options = new CreateCollectionOptions();
    options.timeSeriesOptions(new TimeSeriesOptions("timestamp"));

    db.createCollection("weather", options);
    return "OK";
});

Create a Time Series Collection with CollectionOptions

template.createCollection("weather", CollectionOptions.timeSeries("timestamp"));

Create a Time Series Collection derived from an Annotation

@TimeSeries(collection="weather", timeField = "timestamp")
public class Measurement {

    String id;
    Instant timestamp;
    // ...
}

template.createCollection(Measurement.class);

The snippets above can easily be transferred to the reactive API offering the very same methods. Make sure to properly subscribe to the returned publishers.