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()

Beyond the Java Language

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

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Java development with MongoDB

by James Williams

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