The intention of this recipe is not to explain aggregation but to show you how aggregation can be implemented using the Java client from a Java program. In this recipe, we will aggregate the data based on the state names and get the top five state names by the number of documents that they appear in. We will use the $project
, $group
, $sort
, and $limit
operators for the process.
The test class used for this recipe is com.packtpub.mongo.cookbook.MongoAggregationTest
. To execute the aggregation operations, we need to have a server up and running. A simple single node is what we need. Refer to the Installing single node MongoDB recipe from Chapter 1, Installing and Starting the Server for instructions on how to start the server. The data that we will operate on needs to be imported in the database. The steps to import the data are given in the Creating test data recipe in Chapter 2, Command-line Operations and Indexes. The next...