Using Play with MongoDB

Welcome to the Play Framework/MongoDB playground

Installing the most current mongodb module

cd $playDir/modules
bzr branch lp:~alr/play-mongo/embedded mongo-alr
cd mongo-alr
ant

Changelog

About

Setting up the module

play install mongo

module.crud=${play.path}/modules/mongo-alr

Specifying the mongo server and database

mongo.host=localhost
mongo.port=27017
mongo.database=places

Working with Model classes

A simple model class

@MongoEntity("places")
public class Place extends MongoModel {

	public Place (String name, Double latitude, Double longitude) {
		this.name = name;
		this.location = new Location(latitude, longitude);
	}

	@Required
	public String name;
	
	@MongoEmbedded
	public Location location;
	
	public Double rating = new Double(0);
}

Search by timestamp

@MongoEntity("posts")
public class Post extends MongoModel {

	public Date postedAt;
	...
	
	public Post previous() {
		return Post.find("byPostedAt", new BasicDBObject("$lt", postedAt)).order("by-PostedAt").first();
	}

	public Post next() {
		return Post.find("byPostedAt", new BasicDBObject("$gt", postedAt)).first();
	}

}

Searching by several criterias

@MongoEntity("posts")
public class Post extends MongoModel {

	...
	@MongoEmbedded
	public Set tags;

	public static List findTaggedWith(String... tags) {
		// Equivalent mongodb query
		// db.posts.find({ tags : { $all : [ { name : "tagThree" }, { name : "cool" } ] } } ) 
		BasicDBList tagList = new BasicDBList();
		for (String tag : tags) {
			tagList.add(new BasicDBObject("name", tag));
		}
		DBObject allMatchObj = new BasicDBObject("$all", tagList);
		return Post.find("byTags", allMatchObj).fetch();
    	}
}

Mongos geospatial feature

Adding a geospatial index

@OnApplicationStart
public class EnsureGeoMongoIndex extends Job {

	@Override
	public void doJob() {
		DB db = MongoDB.db();
		DBCollection coll = db.getCollection("places");
		coll.ensureIndex(new BasicDBObject("location", "2d"));
	}
}

Using geospatial queries

@MongoEntity("locations")
public class Location extends MongoModel {

	public Location(Double latitude, Double longitude) {
		this.latitude = latitude;
		this.longitude = longitude;
	}
	
	public Double latitude;
	public Double longitude;
	
}

@MongoEntity("places")
public class Place extends MongoModel {

	public Place (String name, Double latitude, Double longitude) {
		this.name = name;
		this.location = new Location(latitude, longitude);
	}

	@Required
	public String name;
	
	@MongoEmbedded
	public Location location;
	
	public Double rating = new Double(0);
	
	
	public String toString() {
		return name + "@" + location.latitude + "/" + location.longitude;
	}
	
	public static List findNearBy(Double latitude, Double longitude, int limit) {
		// db.places.find( { loc : { $near : [50,50] } } )
		DBObject coordinateObj = new BasicDBObject();
		coordinateObj.put("latitude", latitude);
		coordinateObj.put("longitude", longitude);
		DBObject nearByObj = new BasicDBObject("$near", coordinateObj);
		// Ignore the first, this is your own place, it has always 0 distance
		return Place.find("byLocation", nearByObj).from(1).fetch(limit);
	}

	
	public List findNearBy() {
		return Place.findNearBy(location.latitude, location.longitude, 10);
	}

	public List findNearBy(int limit) {
		return Place.findNearBy(location.latitude, location.longitude, limit);
	}

	
}

    public static void search(String q) {
    	notFoundIfNull(q);
    	Pattern pattern = Pattern.compile(q, Pattern.CASE_INSENSITIVE);
    	List places = Place.find("byName", pattern).fetch();
    	render(places);
    }

    public static void showPlace(String id) {
    	Place place = Place.find("by_id", id).first();
    	List nearbyPlaces = place.findNearBy(5);
    	render(nearbyPlaces, place);
    }

<ul>
#{list nearbyPlaces, as:'nearPlace'}
<li>#{a @Application.showplace(nearPlace._id)}${nearPlace.name}#{/a}, 
  distance is ${nearPlace.distanceTo(place).format("#.##")} km</li>
#{/list}
</ul>

public class PlacesExtensions extends JavaExtensions {

	public static Double distanceTo(Place fromPlace, Place toPlace) {
		return new Double(distance(fromPlace.location.latitude, fromPlace.location.longitude,
				toPlace.location.latitude, toPlace.location.longitude));
	}


	private static double distance(double lat1, double lon1, double lat2, double lon2) {
		double theta = lon1 - lon2;
		double dist = Math.sin(deg2rad(lat1)) * Math.sin(deg2rad(lat2)) + Math.cos(deg2rad(lat1)) * 
			Math.cos(deg2rad(lat2)) * Math.cos(deg2rad(theta));
		
		dist = Math.acos(dist);
		dist = rad2deg(dist) * 60 * 1.1515 * 1.609344;
		
		return dist;
	}

	private static double deg2rad(double deg) {
		return (deg * Math.PI / 180.0);
	}

	private static double rad2deg(double rad) {
		return (rad * 180.0 / Math.PI);
	}

}

Map/Reduce in mongo

A simple map reduce example

@MongoEntity("tags")
public class Tag extends MongoModel {

	@Required
	public String name;

}

@MongoEntity("posts")
public class Post extends MongoModel {
	...
	@MongoEmbedded
	public Set tags;
	...
}

@MongoEntity("tags")
public class Tag extends MongoModel {

	@Required
	public String name;

	/*
	 * Map function: 
	 * function () { this.tags.forEach(function (z) {emit(z.name, {count:1});}); }
	 *
	 * Reduce function:
	 * r = function(key, values){ var total = 0; for ( var i=0; i < values.length; i++ ) { 
	 *           total += values[i].count } ; return { count : total }; }
	 * 
	 * Execute:
	 * res = db.posts.mapReduce(m, r)
	 * 
	 * Show data:
	 * db[res.result].find().sort({ _id : 1 })
	 * 
	 * Drop data:
	 * db[res.result].drop()
     */
	public static List

Lots of stuff still missing

MongoFixtures

GridFS support

Implementing some CRUD module

Test suite

Lazy loading

Using JBoss AOP instead of javassist

Implementing a @MongoTransient annotation

public class Author extends MongoModel {
	...
	@MongoTransient
	public String transientString;	
	...
}

Implementing field name annotations

public class Location extends MongoModel {
	@MongoField("long")
	public Double longitude;
	
	@MongoField("lat")
	public Double latitude;
}

Download examples

• Yabe using mongodb as backend. Uses some queries and Map/Reduce. Download
• BYOQ (Build your own qype). Uses the geospatial indexes and shows a bing map with markers. Also features a small rating calculator job. Download