Intersect in mongodb from two records - mongodb

Question

MongoDb + Spring boot + intersectsArrays
I want to fetch randomly 15 users and know there common interest. Document structure is something like this
{
"_id": {
"$oid": "593f773202338a47584b351e"
},
"interests": [
{
"_id": {
"$oid": "5957933cf3c5f5253ec9476c"
},
"name": "abc1",
"facebookId": "123"
}]
]
}
Need to fetch common interest for each user returned by mongo.
Below is my Spring boot code
Criteria criteria = new Criteria().andOperator(Criteria.where("lastLoginDate").gte(Utility.getDateBeforeDays(lastLoginNewerThan)));
Aggregation agg = Aggregation.newAggregation(new CustomAggregationOperation(maxRecords),
Aggregation.match(criteria),Aggregation.project("id","name")
);
AggregationResults<Users> userResults = operations.aggregate(agg, Users.class, Users.class);
List<Users> users = userResults.getMappedResults();

Answer 1

Looks like Spring Mongo Data api doesn't provide a way to pass a list of values as input to the set intersection operator.
You can use AggressionExpression to provide custom implementation.Include below projection in project stage.
.and(new AggregationExpression() {
#Override
public DBObject toDbObject(AggregationOperationContext context) {
return new BasicDBObject("$setIntersection",
Arrays.<Object> asList(
Arrays.<Object> asList("reading","movies"),
"$interests"));
}
}).as("commonInterests"));
You can wrap the expression as a lambda for Java 8
and(context -> new BasicDBObject("$setIntersection",
Arrays.<Object> asList(
Arrays.<Object> asList("reading","movies"),
"$interests")))
.as("commonInterests");