How can we query array field with size less than some specific value in mongodb using springboot?-CodePudding

My objective is to query the array fields who have size less than 5.

I tried the below solution

MongoDatabase database = mongoClient.getDatabase("Friends");
        MongoCollection<Document> collection = database.getCollection("Friend");

        BasicDBObject filter = new BasicDBObject("MainArray", new BasicDBObject("$lt", new BasicDBObject("$size", 4)));
        collection.find(filter).forEach((Consumer<Document>) doc -> {
//perform operations
}

I want to fetch the fields whose size is less than 4.

If I directly put the size 4 -- new BasicDBObject("$size",4) It did works.

But I want to fetch the fields with array size less than 4 In that case it didn't work.

Please provide your valuable suggestions.

CodePudding user response：

You are not using annotations.

{$expr:{$lt:[{$size:"$MainArray"}, 5]}}

You need to use $expr to use operators in simple find.

Equivalent in BasicDBObject is

new BasicDBObject("$expr", 
       new BasicDBObject("$lt", 
            Arrays<DBObject>.asList(new BasicDBObject("$size", "$MainArray"), 5)
       )
)