Cassandra DataStax Java Driver provides a simple object mapper, which avoids manually converting your domain classes to and from query results.

Example

Run Cassandra server and create a keyspace (my_test_keyspace) as described in this tutorial.

Maven dependency

pom.xml

<dependency>
   <groupId>com.datastax.cassandra</groupId>
   <artifactId>cassandra-driver-mapping</artifactId>
   <version>3.10.2</version>
</dependency>

Creating domain class

Cassandra annotations provided in com.datastax.driver.mapping.annotations package are used to map a table to a Java class:

package com.logicbig.example;

import com.datastax.driver.mapping.annotations.PartitionKey;
import com.datastax.driver.mapping.annotations.Table;

@Table(keyspace = "my_test_keyspace", name = "person")
public class Person {
    @PartitionKey
    private long id;
    private String name;
    private int age;

    public Person() {
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

Using Mapper to save/get/delete Java object to/from table

package com.logicbig.example;

import com.datastax.driver.core.*;
import com.datastax.driver.mapping.Mapper;
import com.datastax.driver.mapping.MappingManager;
import java.util.List;

public class CassandraMappingObjectExample {
    public static void main(String[] args) {
        try (Cluster cluster = Cluster.builder()
                                      .addContactPoint("127.0.0.1")
                                      .withPort(9042)
                                      .withoutJMXReporting()
                                      .build()) {
            Session session = cluster.connect("my_test_keyspace");
            session.execute("CREATE TABLE IF NOT EXISTS "
                    + "my_test_keyspace.PERSON (id bigint PRIMARY KEY, name text, age int)");
            MappingManager manager = new MappingManager(session);
            Mapper<Person> mapper = manager.mapper(Person.class);

            //save person
            mapper.save(new Person("Sandy", 33));
            executeNativeSelectQuery(session);

            //getting via mapper by primary key
            Person person = mapper.get(0L);
            System.out.println(person);

            //getting via mapper by primary key
            mapper.delete(0L);//delete by primary key
            executeNativeSelectQuery(session);

            //dropping table at the end
            session.execute("DROP TABLE my_test_keyspace.PERSON");
        }
    }

    private static void executeNativeSelectQuery(Session session) {
        System.out.println("-- select query --");
        ResultSet rs = session.execute("select * from my_test_keyspace.Person");
        List<Row> rows = rs.all();
        System.out.println("rows: " + rows.size());
        for (Row row : rows) {
            long id = row.getLong("id");
            System.out.println("Id: " + id);
            String name = row.getString("name");
            System.out.println("name: " + name);
            int age = row.getInt("age");
            System.out.println("age: " + age);
        }
    }
}

-- select query --
rows: 1
Id: 0
name: Sandy
age: 33
Person{id=0, name='Sandy', age=33}
-- select query --
rows: 0

Primary key, Partition Key and Clustering key

A primary key uniquely identifies a row.

A partition key is used to lookup a partition which is nothing but a set of rows. This is responsible for data distribution across the nodes.

The Primary Key is equivalent to the Partition Key in a single-field-key (not composite key) table.

The Clustering Key is responsible for data sorting within the partition.

Example Project

Dependencies and Technologies Used:

• cassandra-driver-mapping 3.10.2: Object mapper for the DataStax CQL Java Driver.
• JDK 8
• Maven 3.5.4