com.allanbank.mongodb.builder

Class Aggregate

java.lang.Object

com.allanbank.mongodb.builder.Aggregate

public class Aggregate
extends Object

Aggregate provides support for the aggregate command supporting a pipeline of commands to execute.

Instances of this class are constructed via the inner Aggregate.Builder class. Due to the potential complexity of pipelines and the associated operators the Builder is intended to be used with the various support classes including the Expressions library. For example:

 
  import static com.allanbank.mongodb.builder.AggregationGroupField.set;
  import static com.allanbank.mongodb.builder.AggregationGroupId.id;
  import static com.allanbank.mongodb.builder.AggregationProjectFields.includeWithoutId;
  import static com.allanbank.mongodb.builder.QueryBuilder.where;
  import static com.allanbank.mongodb.builder.Sort.asc;
  import static com.allanbank.mongodb.builder.Sort.desc;
  import static com.allanbank.mongodb.builder.expression.Expressions.field;
  import static com.allanbank.mongodb.builder.expression.Expressions.set;
  
  DocumentBuilder b1 = BuilderFactory.start();
  DocumentBuilder b2 = BuilderFactory.start();
  Aggregate.Builder builder = new Aggregate.Builder();
  
  builder.match(where("state").notEqualTo("NZ"))
          .group(id().addField("state")
                     .addField("city"),
                 set("pop").sum("pop"))
          .sort(asc("pop"))
          .group(id("_id.state"), 
                 set("biggestcity").last("_id.city"),
                 set("biggestpop").last("pop"),
                 set("smallestcity").first("_id.city"),
                 set("smallestpop").first("pop"))
          .project(
                  includeWithoutId(),
                  set("state", field("_id")),
                  set("biggestCity",
                          b1.add(set("name", field("biggestcity"))).add(
                                  set("pop", field("biggestpop")))),
                  set("smallestCity",
                          b2.add(set("name", field("smallestcity"))).add(
                                  set("pop", field("smallestpop")))))
          .sort(desc("biggestCity.pop"));
 
 

See Also:

Example Inspired By

API Notice:

This class is part of the driver's API. Public and protected members will be deprecated for at least 1 non-bugfix release (version numbers are <major>.<minor>.<bugfix>) before being removed or modified.

Copyright ©:

2012, Allanbank Consulting, Inc., All Rights Reserved

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Aggregate.Builder Builder provides the ability to construct aggregate command pipelines.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Aggregate(Aggregate.Builder builder) Creates a new Aggregate.

Method Summary

Methods

Modifier and Type	Method and Description
List<Element>	getPipeline() Returns the pipeline of operations to apply.
ReadPreference	getReadPreference() Returns the ReadPreference specifying which servers may be used to execute the aggregation.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Aggregate

protected Aggregate(Aggregate.Builder builder)

Creates a new Aggregate.

Parameters:

builder - The builder for the Aggregate instance.

Method Detail

getPipeline

public List<Element> getPipeline()

Returns the pipeline of operations to apply.

Returns:

The pipeline of operations to apply.

getReadPreference

public ReadPreference getReadPreference()

Returns the ReadPreference specifying which servers may be used to execute the aggregation.

If null then the MongoCollection instance's ReadPreference will be used.

Returns:

The read preference to use.

See Also:

MongoCollection.getReadPreference()