Finding min and max values with MongoDB Aggregation

Aggregation operations in MongoDB allow you to process documents to produce computed results. An example is to search for a min or max value. For documents that look like this:

  "_id" : ObjectId("5521ae8c0364d302910ec5eb"),
  "color" : "blue",
  "orderDate" : ISODate("2014-07-08T19:53:00Z")
  //other properties

You can find the min/earliest date in the collection for an document with matching color of blue with an aggregation query like this:

{ "$match" : { "color":"blue" } },
{ "$group" : { "_id" : "$color",
first: { "$min" : "$orderDate"},

Implementing this with the Java Driver API looks like this:

DBObject match = new BasicDBObject("$match", new BasicDBObject("color", "blue"));

DBObject groupFields = new BasicDBObject( "_id", "$color");
groupFields.put("orderDate", new BasicDBObject( "$min", "$orderDate"));
DBObject group = new BasicDBObject("$group", groupFields);

List<DBObject> pipeline = Arrays.asList(match, group);

AggregationOutput output = col.aggregate(pipeline);
for (DBObject result : output.results()) {
//iterate results, only 1 for $min

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.