Write Concern

Overview

In this guide, you can learn how to use the Java Reactive Streams driver to specify a write concern. Write concern describes the level of acknowledgment requested from MongoDB for write operations.

You can configure a write concern at the following levels:

• For your MongoDB deployment

• For your database

• For your collection

Configure Write Concern at the Deployment Level

You can configure the write concern at the deployment level in the following ways:

• By creating a MongoClientSettings instance, as shown in the following code:

  MongoClient mongoClient = MongoClients.create(MongoClientSettings.builder()
        .applyConnectionString(new ConnectionString("mongodb://host1,host2"))
        .writeConcern(WriteConcern.MAJORITY)
        .build());

• By creating a ConnectionString instance, as shown in the following code:

  MongoClient mongoClient =
  MongoClients.create("mongodb://host1:27017,host2:27017/?w=majority");

Configure Write Concern at the Database or Collection Level

You can configure the write concern at the database or collection level in the following ways:

• In a MongoDatabase by using the withWriteConcern() method, as shown in the following code:

  MongoDatabase database = mongoClient.getDatabase("test").withWriteConcern(WriteConcern.MAJORITY);

• In a MongoCollection by using the withWriteConcern() method, as shown in the following code:

  MongoCollection<Document> collection = database
      .getCollection("restaurants")
      .withWriteConcern(WriteConcern.MAJORITY);

MongoDatabase and MongoCollection instances are immutable. Calling withWriteConcern() on an existing MongoDatabase or MongoCollection instance returns a new instance and does not affect the instance on which the method is called.

In the following example, the collWithWriteConcern instance has the write concern of majority whereas the read preference of the collection is unaffected:

MongoCollection<Document> collWithWriteConcern = collection
    .withWriteConcern(WriteConcern.MAJORITY);

Combine Read Concern, Read Preference, and Write Concern

You can build MongoClientSettings, MongoDatabase, or MongoCollection instances to include combinations of read concerns, read preferences, and write concerns.

For example, the following code sets all three at the collection level:

Collection = database.getCollection("restaurants")
    .withReadPreference(ReadPreference.primary())
    .withReadConcern(ReadConcern.MAJORITY)
    .withWriteConcern(WriteConcern.MAJORITY);

Additional Information

To learn more about write concerns, see the Write Concern guide in the MongoDB Server manual.