Updating values of given field using expression in mongodb using java

Question

Consider a collection of objects having fields like:

{
    id: // String
    type: //Integer
    score: //Double value
}

I would like to query on collection using type and for returned documents divide their scores by their maximum. Consider following query oject:

DBObject searchQuery = new BasicDBObject("type", 2);
collection.find(searchQuery);

With above query it'll return some documents. I want to get maximum of scores among all those documents and then divide all those documents' score by obtained maximum.

How can I do this??

I could find maximum using aggregation as follows:

String propertyToOperateOn = "score";

DBObject match = new BasicDBObject("$match", searchQuery);

DBObject groups = new BasicDBObject("_id", null);
DBObject operation = new BasicDBObject("$max", "$" + propertyToOperateOn);
groups.put("maximum", operation);

DBObject apply = new BasicDBObject("$group", groups);
AggregationOutput output = mongoConstants.IAScores.aggregate(match, apply);

Here output will contain the maximum value. But then how can I update (divide) all documents' scores by this maximum??

I hope there could be better way to do this task, but I'm unable to get it as I'm very much new to mongodb (or any database as such).

Community · Accepted Answer · 2017-05-23 12:28:59Z

1

This is technically the same issue as "mongodb: java: How to update a field in MongoDB using expression with existing value", but I'll repeat the answer:

At the moment, MongoDB doesn't allow you to update the value of a field according to an existing value of a field. Which means, you can't do the following SQL:

UPDATE foo SET field1 = field1 / 2;

In MongoDB, you will need to do this in your application, but be aware that this is no longer an atomic operation as you need to read and then write.

edited May 23, 2017 at 12:28

CommunityBot

11 silver badge

answered Jul 3, 2013 at 8:35

Derick

36.9k7 gold badges82 silver badges104 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Updating values of given field using expression in mongodb using java

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related