Minimal implementation to reproduce issue where auto-generated interface methods cannot get a DB entity by a nested object id given as a String, although the entity can be obtained by its own id as a String.

The issue is described by questions like this on StackOverflow. It concerns the findByX repository interface methods Spring generates for you. In the case of findById, both String and ObjectId ids work, but in the case of findByNestedObjectId only ids of type ObjectId work.

In this reproduction, I have two DB objects, Entity and NestedEntity, and repositories for both. The repository for Entity contains the following methods:

• findById(String id)
• findById(ObjectId id)
• findByNestedEntityId(String id)
• findByNestedEntityId(ObjectId id)

I aim to show that all methods except findByNestedEntityId(String id) work and return objects while that method returns null.

• Navigate to project directory
• ./gradlew bootrun
• Each method invocation produces a log line informing us whether it returned null or not