spring-projects/spring-data-mongodb

NPE when projecting to an interface using String-based Aggregation Repository Query Methods

fdutton opened this issue · 5 comments

fdutton commented
  1. AbstractMongoQuery.execute() calls ReturnedInterface.getTypeToRead()
  2. ReturnedInterface.getTypeToRead() returns null when the query's result is a closed projection
  3. AbstractMongoQuery.execute() calls StringBasedAggregation.execute()
  4. StringBasedAggregation.execute() calls StringBasedAggregation.isSimpleReturnType() and passes null as the targetType
  5. StringBasedAggregation.isSimpleReturnType() calls MongoSimpleTypes.HOLDER.isSimpleType()
  6. MongoSimpleTypes.HOLDER.isSimpleType() raises a NullPointerException by attempting to invoke type.isEnum() when type is null

This does not happen when projecting to a class.

mp911de commented

If you would like us to spend some time helping you to diagnose the problem, please spend some time describing it and, ideally, providing a minimal yet complete sample that reproduces the problem.
You can share it with us by pushing it to a separate repository on GitHub or by zipping it up and attaching it to this issue.

fdutton commented

I already diagnosed the problem and attempted to describe what is happening step-by-step. I think the root cause is in ReturnedInterface.getTypeToRead as it returns null under certain conditions when it should return a Class that represents the interface used in the projection.

mp911de commented

I already diagnosed the problem and attempted to describe what is happening step-by-step.

I appreciate that you understand the issue. In such a case, care to submit a pull request?

If not, then I'd like to understand the issue too and the way you understand things might be very different that other people understand them.

fdutton commented

The best I can do at the moment is provide a failing unit-test. I attempted a fix but there are other issues preventing interface-based projections and I don't know enough about the inner workings of Spring Data Mongo. In my opinion, the root cause of this issue lies within spring-data-commons but a fix there would probably break some other implementation.

#4840

christophstrobl commented

@fdutton thanks for the testcase.