Add configuration properties for MongoDB's read and write consistency

Summary

Currently, MongoProperties in Spring Boot does not provide a dedicated property for configuring MongoDB read preference. This limits the ability to declaratively set read preference modes and tags via application properties, especially in replica set environments.

Current Workarounds

Using connection URI with readPreference parameter:

spring:
  data:
    mongodb:
      uri: mongodb://localhost:27017/test?readPreference=secondaryPreferred

Or customizing MongoClientSettings via Java configuration

Limitations:

URI-based configuration is less consistent with other MongoDB properties.
Java-based customization increases configuration complexity and reduces clarity for operations teams.

Proposal

Add a readPreference property to MongoProperties, enabling configuration like:

spring:
  data:
    mongodb:
      read-preference: secondaryPreferred

This property would map to the corresponding ReadPreference in the MongoDB Java driver.

Ensure full backward compatibility with existing URI-based configurations.

Optionally support configuration of readPreferenceTags if alignment with advanced use cases is desired.

Use Cases

Applications running on MongoDB replica sets that require secondary or custom read routing.

Environments where configuration consistency and clarity are important (e.g., cloud-native deployments, infrastructure as code).

References

MongoDB Read Preference Documentation

Spring Boot MongoProperties Source

Request

Is there interest in supporting this feature in Spring Boot?

If so, I am willing to contribute a PR with the proposed changes and documentation updates.

Start with spring-boot-project/spring-boot-mongodb/src/main/java/org/springframework/boot/mongodb/autoconfigure/MongoProperties.java, then review the related MongoDB configuration and documentation. Define the property behavior, including compatibility with URI-based settings and whether read preference tags are in scope; done means the property can configure read preference declaratively and the documentation reflects the supported configuration.