how can i cast Resultset object of cassandra in user defined java class object or in ArrayLIst

Question

I am new to Apache Cassandra .

I want to know How to cast a Resultset object to either a user defined list type or a user defined object in java.

I have tried many things but still stuck.

**This is the code" of the method I've tried so far:

public List getOutBoundMessageListFromCassandra(){
   List<XchangeOutboundMessage> list=new ArrayList();
   try {

       cluster = Cluster.builder().addContactPoint(contactPoints).build();

       session = cluster.connect(keySpaceName);

       cassandraOps = new CassandraTemplate(session);

       Select s = QueryBuilder.select().from("XchangeOutboundMessage");
       ResultSet result = session.execute(s);
       list=result.all();
   } catch (Exception e) {
       e.printStackTrace();
   }
   return list;

}

Answer 1

Let's Assume you have the table :

CREATE TABLE xchangeoutboundmessage (
    id timeuuid PRIMARY KEY,
    message text,
    sender bigint
);

And the Associated DTO

public class XchangeOutboundMessage {

    private UUID id;
    private String message;
    private long sender;

    public UUID getId() {
        return id;
    }

    public String getMessage() {
        return message;
    }

    public long getSender() {
        return sender;
    }

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

    public void setMessage(String message) {
        this.message = message;
    }

    public void setSender(long sender) {
        this.sender = sender;
    }

    @Override
    public String toString() {
        return "XchangeOutboundMessage{" + "id=" + id + ", message=" + message + ", sender=" + sender + '}';
    }

}

You can Either Manually get date from row and set value to dto or you can use cassandra-driver-mapping to do this for you.

Using Manual mapping :

for (Row row : result) {
    XchangeOutboundMessage message = new XchangeOutboundMessage();
    message.setId(row.getUUID("id"));
    message.setMessage(row.getString("message"));
    message.setSender(row.getLong("sender"));
    list.add(message);
}

Using cassandra driver mapping :

First Add @Table(name = "XchangeOutboundMessage") Annotation to XchangeOutboundMessage DTO

MappingManager manager = new MappingManager(session);
Mapper<XchangeOutboundMessage> mapper =  manager.mapper(XchangeOutboundMessage.class);
list = mapper.map(result).all();

Note : cassandra-driver-mapping need to add as dependency

By the way these type of query is very inefficient in cassandra, always try to provide partition key in where clause.