Getting MapReduce results on RIAK (using the Java client)

问题

I am storing Person POJOs (4 string fields - id, name, lastUpdate, Data) on RIAK, then trying to fetch these objects with MapReduce.

I am doing it very similar to Basho documentation:

    BucketMapReduce m = riakClient.mapReduce("person");
    m.addMapPhase(new NamedJSFunction("Riak.mapByFields"), true);
    MapReduceResult result = m.execute();
    Collection<Person> tmp = result.getResult(Person.class);

the Person's String constructor is invoked:

public Person(String str){}

(I must have this constructor, otherwise I get an exception for it is missing) In there I get the object as a String - the Object's fields in one string with a strange delimiter.

why am I not getting the object automatically converted to my POJO? do I really need to go over the string and deserialize it? am i doing something wrong?s

回答1:

The JS function you're using doesn't do what you think it does :) It selects objects based on a field with a specific value you have to supply as an argument to the phase.

I think what you're looking for is mapValuesJson which will do what you seem to be wanting to do.

Also, you don't need a constructor at all in your POJO.

The code below should point you in the right direction (obviously this is super-simple with all public fields in the POJO and no annotations):

public class App {

    public static void main( String[] args ) throws IOException, RiakException
    {
        IRiakClient client = RiakFactory.httpClient();
        Bucket b = client.fetchBucket("test_mr").execute();

        b.store("myobject", new Person()).execute();
        IRiakObject o = b.fetch("myobject").execute();
        System.out.println(o.getValueAsString());


        BucketMapReduce m = client.mapReduce("test_mr");
        m.addMapPhase(new NamedJSFunction("Riak.mapValuesJson"), true);
        MapReduceResult result = m.execute();
        System.out.println(result.getResultRaw());
        Collection<Person> tmp = result.getResult(Person.class);

        for (Person p : tmp)
        {
            System.out.println(p.data);
        }


        client.shutdown();
    }
}

class Person 
{
    public String id = "12345";
    public String name = "my name";
    public String lastUpdate = "some time";
    public String data = "some data";


}

来源：https://stackoverflow.com/questions/11543447/getting-mapreduce-results-on-riak-using-the-java-client

标签

java

MapReduce

riak