The intention of this recipe is not to explain aggregation but to show how aggregation can be implemented using a 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 they appear in. We will make use of 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 will need. Refer to the Single node installation of MongoDB recipe in Chapter 1, Installing and Starting the MongoDB Server, to learn how to start the server. The data on which we will operate 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 step is...