`MongoTemplate.aggregate(…, Map.class)` considers `Map` an entity projection

[nealeu]

This appears to be a regression when migrating to Spring Data MongoDB 5.0.0, as there's nothing in the release notes about this.

Everywhere we project to a Map, when we do:

var result = mongoOperations.aggregate(aggregation, Map.class)

we get

No mapping metadata found for java.lang.Object
org.springframework.data.mapping.MappingException: No mapping metadata found for java.lang.Object
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.doReadProjection(MappingMongoConverter.java:397)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.project(MappingMongoConverter.java:366)

WORKAROUND: In our case we can replace the Map with a record with the fields we need.

[christophstrobl]

Thank you for getting in touch. Please take the time to provide a complete minimal sample (something that we can unzip or git clone, build, and deploy) that reproduces the problem.

[nealeu]

Thanks. I'm aware, but also it may not happen before I go on holiday, but I wanted to ensure it's discoverable by others.

[nealeu]

Here you go https://github.com/nealeu/MongoMapProjectionTest

[nealeu]

Fast work @christophstrobl. Looks sane. Thank you.