cassandra-jom

• An easy to use java object mapper, built around DataStax's Java CQL driver.
• It can automatically create tables and add columns from your cql annotated domain objects.
• jom can auto-generate UUID
• Composite keys are well supported. Keys can be designated as either partition key or cluster keys, using the CqlId annotation.
• Automatically converts Java camel-casing naming to cql style naming. For example, if you have an entity CarModel, the corresponding table name will be car_model.
• Embed objects within your entity. For example, you can embed Address object inside your User entity.
• JPA style annotations. CqlEntity, CqlId, CqlAutoGen, CqlEmbed, CqlStoreAsJson
• Cassandra has very limited querying capabilities. Jom gets round the limitation by implementing filter feature.
• In cassandra, it is efficient to update just the modified fields. Column level updates can be done, using updateColumn method.
• Cassandra light weight transaction support. Inserts, updates and deletes can be done in batches.
• Counter column support with @CqlColumn(dataType=DataType.COUNTER) annotation on any nemeric fields
• Release 1.3.2 is a stable release. The project that uses cassandra jom is live and communicates to a 3 node Datastax Enterprise cassandra cluster, using SSL.

Get Started

* Refer to the Project Wiki to get started with Cassandra JOM.

Maven Dependency

The jar files are published in maven repository. http://mvnrepository.com/artifact/org.w3cloud.api/cassandra-jom/1.3.4

<dependency>
  <groupId>org.w3cloud.api</groupId>
  <artifactId>cassandra-jom</artifactId>
  <version>1.3.4</version>
</dependency>

Your entity object

package org.w3cloud.jom.testmodels;
import java.util.UUID;
import org.w3cloud.jom.annotations.CqlAutoGen;
import org.w3cloud.jom.annotations.CqlEntity;
import org.w3cloud.jom.annotations.CqlId;
@CqlEntity
public class CarModel {
@CqlId(idType=IdType.PARTITION_KEY) //another idType is CLUSTER_KEY
@CqlAutoGen
private UUID id;
private String make;
private String modelName;
@CqlIndex
private int modelYear;
public UUID getId(){
return id;
}
public void setId(UUID id){
this.id=id;
}
..... Other getters and setters
}

Insert, update and find your entity

			Properties props=new Properties();
			//You can also pass multiple contact points and port numbers.
			// Example: props.put("cql.contactpoints", "localhost:9042,anotherhost:9042");
			props.put("cql.contactpoints", "localhost");
			props.put("cql.keyspace","jom_test");
			props.put("cql.synctableschema", "true");
			//if you have more than one package to scan,
			//Pass a comma separated list
			props.put("cql.packagestoscan", "org.w3cloud.jom.testmodels");
			//Store EntityManager as a static variable at the applicaiton level.
			CqlEntityManager em=CqlEntityManagerFactory.createEntityManger(props);
			CarModel carModel=new CarModel();
			carModel.setMake("Mazda");
			carModel.setModelYear(2015);
			carModel.setModelName("3");
			em.insert(carModel);
			carModel.setModelName("Cx5");
			em.update(carModel);
			ListcarModels=em.findAll(CqlBuilder.select(CarModel.class).
				field("modelYear").eq(2015);
			//Update only one coloumn; Use this approach only if 
			//you are sure about the modified coloumns. 
			//In cassandra this approach is more effiecient
			carModel.setModelName("6");
			em.updateColumn(carModel, CqlBuilder.update(CarModel.class)
				.field("modelName").set(carModel.getModelName()));
			

For Further deails, refer to project wiki.

Upcoming release

• No planned release.

Caution

• CqlStoreAsJson annotation does not work well with Lists. Do your own serilization and de-seriazation, if needed with gson. Serilization is straight-forward. For de-serialization, use the following technique:

  order.orderItems=gson.fromJson(order.orderItemsJson,new TypeToken<List<OrderItem>>(){}.getType());

• Do not use CqlIndex. Cassandra encourages to use link table for queries instead of indexing a column.
• jom does not support casssandra datatypes like map, list and set.

Contribute

• Please post your comments on our cassandra-jom blog page: http://www.w3cloud.org/cassandra-jom
• Please report bugs, by creating an issue.