geode-docs/developing/query_additional/query_on_a_single_node.html.md.erb

---
title:  Querying a Partitioned Region on a Single Node
---

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To direct a query to specific partitioned region node, you can execute the query within a function. Use the following steps:

1.  Implement a function which executes a query using RegionFunctionContext.

    ``` pre
    /**
     * This function executes a query using its RegionFunctionContext
     * which provides a filter on data which should be queried.
     *
     */
    public class MyFunction extends FunctionAdapter {

        private final String id;

        @Override
        public void execute(FunctionContext context) {

          Cache cache = CacheFactory.getAnyInstance();
          QueryService queryService = cache.getQueryService();

          String qstr = (String) context.getArguments();

          try {
            Query query = queryService.newQuery(qstr);

            //If function is executed on region, context is RegionFunctionContext
            RegionFunctionContext rContext = (RegionFunctionContext)context;

            SelectResults results = (SelectResults) query.execute(rContext)

            //Send the results to function caller node.
            context.getResultSender().sendResult((ArrayList) (results).asList());
            context.getResultSender().lastResult(null);

          } catch (Exception e) {
            throw new FunctionException(e);
          }
        }

        @Override
        public boolean hasResult() {
          return true;
        }

        @Override
        public boolean isHA() {
          return false;
        }


        public MyFunction(String id) {
          super();
          this.id = id;
        }

        @Override
        public String getId() {
          return this.id;
        }
      }
    ```

2.  Decide on the data you want to query. Based on this decision, you can use `PartitionResolver` to configure the organization of buckets to be queried in the Partitioned Region.

    For example, let's say that you have defined the PortfolioKey class:

    ``` pre
    public class PortfolioKey implements DataSerializable {
      private int id;
      private long startValidTime;
      private long endValidTime
      private long writtenTime
      
      public int getId() {
        return this.id;
      }
    ...
    }
    ```

    You could use the `MyPartitionResolver` to store all keys with the same ID in the same bucket. This `PartitionResolver` has to be configured at the time of Partition Region creation either declaratively using xml OR using APIs. See [Configuring Partitioned Regions](../partitioned_regions/managing_partitioned_regions.html#configure_partitioned_regions) for more information.

    ``` pre
    /** This resolver returns the value of the ID field in the key. With this resolver, 
     * all Portfolios using the same ID are colocated in the same bucket.
     */
    public class MyPartitionResolver implements PartitionResolver, Declarable {

       public Serializable getRoutingObject(EntryOperation operation) {
       return operation.getKey().getId();
    }
    ```

3.  Execute the function on a client or any other node by setting the filter in the function call.

    ``` pre
    /**
     * Execute MyFunction for query on specified keys.
     *
     */
    public class TestFunctionQuery {

      public static void main(String[] args) {

        ResultCollector rcollector = null;
        PortfolioKey portfolioKey1 = ...;

        //Filter data based on portfolioKey1 which is the key used in 
        //region.put(portfolioKey1, portfolio1);
        Set filter = Collections.singleton(portfolioKey1);

        //Query to get all positions for portfolio ID = 1
        String qStr = "SELECT positions FROM /myPartitionRegion WHERE ID = 1";

        try {
          Function func = new MyFunction("testFunction");

          Region region = CacheFactory.getAnyInstance().getRegion("myPartitionRegion");

          //Function will be routed to one node containing the bucket
          //for ID=1 and query will execute on that bucket.
          rcollector = FunctionService
              .onRegion(region)
              .setArguments(qStr)
              .withFilter(filter)
              .execute(func);

          Object result = rcollector.getResult();

          //Results from one or multiple nodes.
          ArrayList resultList = (ArrayList)result;

          List queryResults = new ArrayList();

          if (resultList.size()!=0) {
            for (Object obj: resultList) {
              if (obj != null) {
                queryResults.addAll((ArrayList)obj);
              }
            }
          }
          printResults(queryResults);

        } catch (FunctionException ex) {
            getLogger().info(ex);
        }
      }
    }
    ```