Databases and Collections

Overview

In this guide, you can learn how to interact with MongoDB databases and collections by using the Scala driver.

MongoDB organizes data into a hierarchy of the following levels:

• Databases: Top-level data structures in a MongoDB deployment that store collections.

• Collections: Groups of MongoDB documents. They are analogous to tables in relational databases.

• Documents: Units that store literal data such as string, numbers, dates, and other embedded documents. For more information about document field types and structure, see the Documents guide in the MongoDB Server manual.

Access a Database

Access a database by calling the getDatabase() method on a MongoClient instance.

The following example accesses a database named "test_database":

val database = mongoClient.getDatabase("test_database")

Access a Collection

Access a collection by calling the getCollection() method on a MongoDatabase instance.

The following example accesses a collection named "test_collection":

val collection = database.getCollection("test_collection")

Create a Collection

Use the createCollection() method on a MongoDatabase instance to explicitly create a collection in a database.

The following example creates a collection named "example_collection":

val createObservable = database.createCollection("example_collection")
Await.result(createObservable.toFuture(), Duration(10, TimeUnit.SECONDS))

You can specify collection options, such as maximum size and document validation rules, by passing a CreateCollectionOptions instance to the createCollection() method. For a full list of optional parameters, see the create command documentation in the MongoDB Server manual.

Get a List of Collections

You can query for a list of collections in a database by calling the listCollections() method of a MongoDatabase instance.

The following example lists all collections in a database:

val results = Await.result(database.listCollections().toFuture(), Duration(10, TimeUnit.SECONDS))
results.foreach(println)

Iterable((name,BsonString{value='test_collection'}), (type,BsonString{value='collection'}), ... )
Iterable((name,BsonString{value='example_collection'}), (type,BsonString{value='collection'}), ... )

To query for only the names of the collections in the database, call the listCollectionNames() method as follows:

val results = Await.result(database.listCollectionNames().toFuture(), Duration(10, TimeUnit.SECONDS))
results.foreach(println)

test_collection
example_collection

Delete a Collection

You can delete a collection by calling the drop() method on a MongoCollection instance.

The following example deletes the test_collection collection:

val deleteObservable = database.getCollection("test_collection").drop()
Await.result(deleteObservable.toFuture(), Duration(10, TimeUnit.SECONDS))

Delete a Database

You can delete a database by calling the drop() method on a MongoDatabase instance.

The following example deletes the test_database database:

var database = mongoClient.getDatabase("test_database")
val deleteObservable = database.drop()
Await.result(deleteObservable.toFuture(), Duration(10, TimeUnit.SECONDS))

Configure Read and Write Operations

You can control how the driver routes read operations by setting a read preference. You can also control options for how the driver waits for acknowledgment of read and write operations on a replica set by setting a read concern and a write concern.

By default, databases inherit these settings from the MongoClient instance, and collections inherit them from the database. However, you can change these settings on your database by using the withReadPreference() method.

The following example accesses a database while specifying the read preference of the database as secondary:

val databaseWithReadPrefs =
    mongoClient.getDatabase("test_database").withReadPreference(ReadPreference.secondary())

You can also change the read and write settings on your collections by using the withReadPreference() method. The following example shows how to access a collection while specifying the read preference of the collection as secondary:

val collectionWithReadPrefs =
    database.getCollection("test_collection").withReadPreference(ReadPreference.secondary())

To learn more about the read and write settings, see the following guides in the MongoDB Server manual:

• Read Preference

• Read Concern

• Write Concern

val tag1 = new Tag("dc", "ny")
val tag2 = new Tag("dc", "sf")
val tagSet = new TagSet(List(tag1, tag2).asJava)
val connectionString = ConnectionString("<connection string URI>")
val readPreference = ReadPreference.primaryPreferred(tagSet)
val mongoClientSettings = MongoClientSettings.builder()
  .applyConnectionString(connectionString)
  .readPreference(readPreference)
  .build()
val clientWithTags = MongoClient(mongoClientSettings)

val connectionString = ConnectionString("mongodb://localhost:27017")
val mongoClientSettings = MongoClientSettings.builder()
  .applyConnectionString(connectionString)
  .applyToClusterSettings(builder => builder.localThreshold(35, TimeUnit.MILLISECONDS))
  .build()
val client = MongoClient(mongoClientSettings)

API Documentation

To learn more about any of the types or methods discussed in this guide, see the following API documentation:

• MongoClient

• MongoDatabase

• MongoCollection

• CreateCollectionOptions

• ClusterSettings

• MongoClientSettings