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

Question

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.

Gibbs · Accepted Answer · 2022-05-23 16:36:17Z

1

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)
       )
)

edited May 23, 2022 at 16:36

answered May 23, 2022 at 15:48

Gibbs

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11 Comments

Rishabh Over a year ago

Hey thanks this looks promising I do remember this works in mongodb ...but it's giving error at Arrays<DBObject>. Have I missed something? Do we need to import something? It's giving unexpected token, Expression expected, Cannot resolve DBObject.

Gibbs Over a year ago

You can use BasicDBObject in place of DBObject

Rishabh Over a year ago

Now it's showing Expression expected, ')' expected, ;expected at Arrays<BasicDBObject>

Gibbs Over a year ago

Please add one extra ) at the end. Updating the answer

Rishabh Over a year ago

Okay ..sure man understood Thanks for helping And sorry for the inconvenience caused. I really appreciate you for helping me. I will try to edit the question again and will mark your answer as correct. Thanks

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