This topic explains how to perform an equi-join query on partitioned regions in VMware Tanzu GemFire.
To perform equi-join operations on partitioned regions or partitioned regions and replicated regions, you must use the query.execute method and supply it with a function execution context. You must use Tanzu GemFire’s FunctionService executor because join operations are not directly supported for partitioned regions without providing a function execution context.
For more information about partitioned region query limitations, see Partitioned Region Query Restrictions.
Example equi-join query:
SELECT DISTINCT * FROM /QueryRegion1 r1,
/QueryRegion2 r2 WHERE r1.ID = r2.ID
In this example QueryRegion2 is colocated with QueryRegion1, and both regions have same type of data objects.
On the server side:
Function prQueryFunction1 = new QueryFunction();
FunctionService.registerFunction(prQueryFunction1);
public class QueryFunction extends FunctionAdapter {
@Override
public void execute(FunctionContext context) {
Cache cache = CacheFactory.getAnyInstance();
QueryService queryService = cache.getQueryService();
ArrayList allQueryResults = new ArrayList();
ArrayList arguments = (ArrayList)(context.getArguments());
String qstr = (String)arguments.get(0);
try {
Query query = queryService.newQuery(qstr);
SelectResults result = (SelectResults)query
.execute((RegionFunctionContext)context);
ArrayList arrayResult = (ArrayList)result.asList();
context.getResultSender().sendResult((ArrayList)result.asList());
context.getResultSender().lastResult(null);
} catch (Exception e) {
// handle exception
}
}
}
On the server side, Query.execute() operates on the local data of the partitioned region.
On the client side:
Function function = new QueryFunction();
String queryString = "SELECT DISTINCT * FROM /QueryRegion1 r1,
/QueryRegion2 r2 WHERE r1.ID = r2.ID";
ArrayList argList = new ArrayList();
argList.add(queryString);
Object result = FunctionService.onRegion(CacheFactory.getAnyInstance()
.getRegion("QueryRegion1" ))
.setArguments(argList).execute(function).getResult();
ArrayList resultList = (ArrayList)result;
resultList.trimToSize();
List queryResults = null;
if (resultList.size() != 0) {
queryResults = new ArrayList();
for (Object obj : resultList) {
if (obj != null ) {
queryResults.addAll((ArrayList)obj);
}
}
}
On the client side, you can specify a bucket filter while invoking FunctionService.onRegion(). In this case, the query engine relies on FunctionService to direct the query to specific nodes.
Additional Notes on Using the Query.execute and RegionFunctionContext APIs
You can also pass multiple parameters (besides the query itself) to the query function by specifying the parameters in the client-side code (FunctionService.onRegion(..).setArguments()). Then you can handle the parameters inside the function on the server side using context.getArguments. It does not matter in which order you specify the parameters as long as you match the parameter handling order on the server with the order specified in the client.
