Java development with MongoDB

Java Development with
MongoDB
James Williams
Software Engineer, BT/Ribbit

Agenda

Java Driver basics
Making Connections
Managing Collections
BasicDBObjectBuilder
Document Queries
GridFS
Morphia
Beyond the Java language
Groovy utilities
Grails plugin

Making a Connection

import com.mongodb.Mongo;
import com.mongodb.DB;

Mongo m = new Mongo();
Mongo m = new Mongo( "localhost" );
Mongo m = new Mongo( "localhost" , 27017 );

DB db = m.getDB( "mydb" );

Working with Collections

Getting all collections in the database
Set<String> colls = db.getCollectionNames();
for (String s : colls) {
System.out.println(s);
}
Getting a single collection
DBCollection coll = db.getCollection("testCollection")

Inserting Documents

BasicDBObject doc = new BasicDBObject();
doc.put("name", "MongoDB");
doc.put("type", "database");
doc.put("count", 1);

BasicDBObject info = new BasicDBObject();
info.put("x", 203);
info.put("y", 102);
doc.put("info", info);
coll.insert(doc);

BasicDBObjectBuilder

Utility for building objects
Can coerce Maps (and possibly JSON*) to DBObjects
Example:
BasicDBObjectBuilder.start()
.add( "name" , "eliot" )
.add( "number" , 17 )
.get();

Document Queries

DBObject myDoc = coll.findOne();
// can also use
BasicDBObject query = new BasicDBObject(); query.put("i", 71);
DBCursor cur = coll.find(query);

GridFS

mechanism for storing files larger than 4MB
files are chunked allowing fetching of a portion or out of
order
chunking is mostly transparent to underlying operating
system
can store files in buckets, a MongoDB metaphor for folders
default is the fs bucket

Saving a file to GridFS

def mongo = new Mongo(host)
def gridfs = new GridFS(mongo.getDB("db"))

def save(inputStream, contentType, filename) {
def inputFile = gridfs.createFile(inputStream)
inputFile.setContentType(contentType)
inputFile.setFilename(filename)
inputFile.save()
}

Retrieving/Deleting a file

def retrieveFile(String filename) {
return gridfs.findOne(filename)
}

def deleteFile(String filename) {
gridfs.remove(filename)
}

Morphia

Apache 2 Licensed
brings Hibernate/JPA paradigms to MongoDB
allows annotating of POJOs to make converting them
between MongoDB and Java very easy
supports DAO abstractions
offers type-safe query support
compatible with GWT, Guice, Spring, and DI frameworks

Morphia Annotations

@Id
@Entity
@Embedded
@Reference
@Indexed
@Serialized
@Property

Creating a Morphia POJO

import com.google.code.morphia.annotations.*;

@Entity("collectionName")
public class Contact {
@Id
private String id; //generated by MongoDB

private String firstName;
private String lastName;
@Embedded
private List<PhoneNumber> phoneNumbers;

// getters and setters
}

Mapping a POJO to a Mongo doc

Morphia morphia = ...;
Mongo mongo = ...;
DB db = mongo.getDB("contacts");

Contact contact = ...;

// map the contact to a DBObject
DBObject contactObj = morphia.toDBObject(contact);

db.getCollection("personal").save(contactObj);

Getting a POJO from a Mongo doc

Morphia morphia = ...;
Mongo mongo = ...;
DB db = mongo.getDB("contacts");

String contactId = ...;

//load the object from the collection
BasicDBObject idObj = new BasicDBObject(
"_id", new ObjectId(contactId)
);
BasicDBObject obj = (BasicDBObject)
db.getCollection("personal").findOne(idObj);
Contact contact = morphia.fromDBObject(Contact.class, obj);

DAOs

Encapsulate saving and retrieving objects
Auto-converts to and from POJOs
Can provide constraints on searches
Key functions:
get(<mongoId>)
find() or find(constraints)
findOne(constraints)
deleteById(<mongoId>)

DAO Example

import com.mongodb.Mongo
import com.google.code.morphia.*

class EntryDAO extends DAO<BlogEntry,String> {
public EntryDAO(Morphia morphia, Mongo mongo) {
super(mongo, morphia, "entries")
}
}

Constraints Examples

dao.find(new Constraints() .
orderByDesc("dateCreated")
).asList()

dao.find(
new Constraints()
.field("dateCreated").greaterThanOrEqualTo(date).field("title").
equalTo(params.title)
).asList()

MongoDB with Groovy

Metaprogramming with MongoDB can reduce LOC
Dynamic finders
Fluent interface mirroring Ruby and Python

Groovy + MongoDB

Java
BasicDBObject doc = new BasicDBObject();
doc.put("name", "MongoDB");
doc.put("type", "database");
doc.put("count", 1);
coll.insert(doc);

Groovier
def doc = [name:"MongoDB",type:"database", count:1, info:
[x:203, y:102] ] as BasicDBObject
coll.insert(doc)

Grooviest (using groovy-mongo)
coll.insert([name:"MongoDB", type:"database", info: [x:203, y:102]])

Dynamic Finders

can build complex queries at runtime
can even reach into objects for addition query parameters

Ex. collection.findByAuthorAndPostCreatedGreaterThan(...)
collection.findByComments_CreatedOn(...)

How dynamic finders work

Groovy receives the request for the method
The method is not found (invoking methodMissing)
The method name used to construct a query template
The method is cached
The method is invoked with the parameters
Future invocations use the cached method

MongoDB Grails Plugin

Replaces JDBC layer in Grails applications
Can use dynamic finders
Requires only slight modifications to domain classes
http://github.com/mpriatel/mongodb-grails

Links

Personal Blog: http://jameswilliams.be/blog
Twitter: http://twitter.com/ecspike

Morphia: http://code.google.com/p/morphia
Utilities for Groovy: http://github.com/jwill/groovy-mongo
MongoDB Grails plugin: http://github.
com/mpriatel/mongodb-grails

Java development with MongoDB

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