Spring Data and MongoDb aggregation examples

I've faced recently with some not trivial mongo aggregation queries and found there are not so many examples available, so main source is official docs https://docs.spring.io/spring-data/mongodb/docs/current/reference/html/#introduction

also was useful tests of the Spring Framework:

https://github.com/spring-projects/spring-data-mongodb/blob/master/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/AggregationTests.java

https://github.com/spring-projects/spring-data-mongodb/blob/master/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/ProjectionOperationUnitTests.java

use to profile query
db.events.explain("executionStats").aggregate("query")