mongo-aggregator

Introduction

This library implements a fluent Java API for MongoDB Aggregation Framework. The
MongoDB Aggregation framework processes data records and returns computed
result. The library implements the aggregation pipeline.

Usage

Actually, the MongoDB Java driver does not support any form of fluent interface to features of the aggregation framework. The mongo-aggregator library enables you to easily create an aggregation pipeline, in a single Java statement.

For example, take the definition of the following pipeline.

Aggregator
    .of(embeddedMongo.mongoClient().getDatabase(DATABASE))
    .collection(COLLECTION)
    .filter(eq("name", "MongoDB"))
    .projection(project(fields(excludeId(), include("name", "count"))))
    .groupBy(group("$name", new BsonField("total", new BasicDBObject("$sum", "$count"))))
    .execute(documents -> {
        List<Document> list = new ArrayList<>();
        for (Document doc: documents) {
            list.add(doc);
        }
        return list;
    });

Giving to the of method an instance of MongoDatabase, you create an empty pipeline.
Once you have a pipeline, provide through the method collection the name of the collection
you want to use.

Well, it’s time to populate the pipeline. By now, the library supports only pipelines built of exactly
one filter stage, one projection stage and one group by stage. In future versions we are plan to manage also different kinds of pipelines

The filter stage should be provided using the filter method. This method accepts a Bson object. Use
com.mongodb.client.model.Filters
class and its methods to create a valid filters.

Likewise, the projection stage should be provided by the projection method. Also this method accept a Bson
object as input. To create a valid projection stage, please use the classes com.mongodb.client.model.Aggregates
and com.mongodb.client.model.Projections and their relative methods.

Finally the group by stage should be provided by the groupBy method. Refer to the aggregation framework documentation
to understand the right structure of the document to pass to the method.

To consume the result of the aggregation pipeline, provide a proper function to the execute method. The function should
transform an AggregateIterable<Document>, which is the result of the execution of the aggregagtion pipeline, in another type of
interest.

By now, the library uses the synchronous version of the MongoDB Java driver. Future versions will support also the
asynchronous version of the driver.

Installation

The library is built using Maven 3. To build the archive containing the library, simply type the following command:

mvn clean install

To execute only provided tests, type instead

mvn test