MongoDB is an open source document-oriented NoSQL database system which stores data as JSON-like documents with dynamic schemas.  As it doesn't store data in tables as is done in the usual relational database setup, it doesn't map well to the JPA way of storing data. Morphia is an open source lightweight type-safe library designed to bridge the gap between the MongoDB Java driver and domain objects. It can be an alternative to SpringData if you're not using the Spring Framework to interact with MongoDB.

This post will cover the basics of persisting and querying entities along the lines of JPA by using Morphia and a MongoDB database instance.

There are four POJOs this example will be using. First we have BaseEntity which is an abstract class containing the Id and Version fields:

package com.city81.mongodb.morphia.entity;
 
import org.bson.types.ObjectId;
import com.google.code.morphia.annotations.Id;
import com.google.code.morphia.annotations.Property;
import com.google.code.morphia.annotations.Version;
 
public abstract class BaseEntity {
 
    @Id
    @Property("id")
    protected ObjectId id;
 
    @Version
    @Property("version")
    private Long version;
 
    public BaseEntity() {
        super();
    }
 
    public ObjectId getId() {
        return id;
    }
 
    public void setId(ObjectId id) {
        this.id = id;
    }
 
    public Long getVersion() {
        return version;
    }
 
    public void setVersion(Long version) {
        this.version = version;
    }
 
}

Whereas JPA would use @Column to rename the attribute, Morphia uses @Property. Another difference is that @Property needs to be on the variable whereas @Column can be on the variable or the get method.

The main entity we want to persist is the Customer class:

package com.city81.mongodb.morphia.entity;
 
import java.util.List;
import com.google.code.morphia.annotations.Embedded;
import com.google.code.morphia.annotations.Entity;
 
@Entity
public class Customer extends BaseEntity {
 
    private String name;
    private List<Account> accounts;
    @Embedded
    private Address address;
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public List<Account> getAccounts() {
        return accounts;
    }
 
    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }
 
    public Address getAddress() {
        return address;
    }
 
    public void setAddress(Address address) {
        this.address = address;
    }
 
}

As with JPA, the POJO is annotated with @Entity. The class also shows an example of @Embedded:

The Address class is also annotated with @Embedded as shown below:

package com.city81.mongodb.morphia.entity;
 
import com.google.code.morphia.annotations.Embedded;
 
@Embedded
public class Address {
 
    private String number;
    private String street;
    private String town;
    private String postcode;
 
    public String getNumber() {
        return number;
    }
 
    public void setNumber(String number) {
        this.number = number;
    }
 
    public String getStreet() {
        return street;
    }
 
    public void setStreet(String street) {
        this.street = street;
    }
 
    public String getTown() {
        return town;
    }
 
    public void setTown(String town) {
        this.town = town;
    }
 
    public String getPostcode() {
        return postcode;
    }
 
    public void setPostcode(String postcode) {
        this.postcode = postcode;
    }
 
}

Finally, we have the Account class of which the customer class has a collection of:

package com.city81.mongodb.morphia.entity;
 
import com.google.code.morphia.annotations.Entity;
 
@Entity
public class Account extends BaseEntity {
 
    private String name;
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
}

The above show only a small subset of what annotations can be applied to domain classes. More can be found at http://code.google.com/p/morphia/wiki/AllAnnotations

The Example class shown below goes through the steps involved in connecting to the MongoDB instance, populating the entities, persisting them and then retrieving them:

package com.city81.mongodb.morphia;
 
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;
import com.city81.mongodb.morphia.entity.Account;
import com.city81.mongodb.morphia.entity.Address;
import com.city81.mongodb.morphia.entity.Customer;
import com.google.code.morphia.Datastore;
import com.google.code.morphia.Key;
import com.google.code.morphia.Morphia;
import com.mongodb.Mongo;
import com.mongodb.MongoException;
 
/**
 * A MongoDB and Morphia Example
 *
 */
public class Example {
 
    public static void main( String[] args ) throws UnknownHostException, MongoException {
 
     String dbName = new String("bank");
     Mongo mongo = new Mongo();
     Morphia morphia = new Morphia();
     Datastore datastore = morphia.createDatastore(mongo, dbName);      
 
     morphia.mapPackage("com.city81.mongodb.morphia.entity");
         
     Address address = new Address();
     address.setNumber("81");
     address.setStreet("Mongo Street");
     address.setTown("City");
     address.setPostcode("CT81 1DB"); 
 
     Account account = new Account();
     account.setName("Personal Account");
 
     List<Account> accounts = new ArrayList<Account>();
     accounts.add(account); 
 
     Customer customer = new Customer();
     customer.setAddress(address);
     customer.setName("Mr Bank Customer");
     customer.setAccounts(accounts);
     
     Key<Customer> savedCustomer = datastore.save(customer);   
     System.out.println(savedCustomer.getId());
 
}

Executing the first few lines will result in the creation of a Datastore. This interface will provide the ability to get, delete and save objects in the 'bank' MongoDB instance.

The mapPackage method call on the morphia object determines what objects are mapped by that instance of Morphia. In this case all those in the package supplied. Other alternatives exist to map classes, including the method map which takes a single class (this method can be chained as the returning object is the morphia object), or passing a Set of classes to the Morphia constructor.

After creating instances of the entities, they can be saved by calling save on the datastore instance and can be found using the primary key via the get method. The output from the Example class would look something like the below:

11-Jul-2012 13:20:06 com.google.code.morphia.logging.MorphiaLoggerFactory chooseLoggerFactory
INFO: LoggerImplFactory set to com.google.code.morphia.logging.jdk.JDKLoggerFactory
4ffd6f7662109325c6eea24f
Mr Bank Customer

There are many other methods on the Datastore interface and they can be found along with the other Javadocs at http://morphia.googlecode.com/svn/site/morphia/apidocs/index.html

An alternative to using the Datastore directly is to use the built in DAO support. This can be done by extending the BasicDAO class as shown below for the Customer entity:

package com.city81.mongodb.morphia.dao;
 
import com.city81.mongodb.morphia.entity.Customer;
import com.google.code.morphia.Morphia;
import com.google.code.morphia.dao.BasicDAO;
import com.mongodb.Mongo;
 
public class CustomerDAO extends BasicDAO<Customer, String> {   
 
    public CustomerDAO(Morphia morphia, Mongo mongo, String dbName) {       
        super(mongo, morphia, dbName);   
    }
 
}

To then make use of this, the Example class can be changed (and enhanced to show a query and a delete):

...
 
     CustomerDAO customerDAO = new CustomerDAO(morphia, mongo, dbName);
     customerDAO.save(customer);
 
     Query<Customer> query = datastore.createQuery(Customer.class);
     query.and(       
       query.criteria("accounts.name").equal("Personal Account"),     
       query.criteria("address.number").equal("81"),       
       query.criteria("name").contains("Bank")
     );      
 
     QueryResults<Customer> retrievedCustomers =  customerDAO.find(query);  
 
     for (Customer retrievedCustomer : retrievedCustomers) {
         System.out.println(retrievedCustomer.getName());   
         System.out.println(retrievedCustomer.getAddress().getPostcode());   
         System.out.println(retrievedCustomer.getAccounts().get(0).getName());
         customerDAO.delete(retrievedCustomer);
     } 
     
...

With the output from running the above shown below:

11-Jul-2012 13:30:46 com.google.code.morphia.logging.MorphiaLoggerFactory chooseLoggerFactory
INFO: LoggerImplFactory set to com.google.code.morphia.logging.jdk.JDKLoggerFactory
Mr Bank Customer
CT81 1DB
Personal Account

This post only covers a few brief basics of Morphia but shows how it can help bridge the gap between JPA and NoSQL.