/// <summary>
/// This method executes the map reduce task
/// </summary>
/// <returns> Returns the tracker through which task can be monitored and result can be fetched </returns>
private ITrackableTask ExecuteMapReduceTask()
{
// Create InitParams for the MapReduce task, i.e., set mapper, combiner and reducer
// Mapper is a must, other two are optional.
MapReduceInitParams initParams = new MapReduceInitParams("NosDB.Samples.MapReduceImplementation.Mapper, NosDB.Samples.MapReduceImplementation, Version=1.0.0.0, Culture=neutral", "mapreduceimpl");
initParams.Combiner = "NosDB.Samples.MapReduceImplementation.CombinerFactory, NosDB.Samples.MapReduceImplementation, Version=1.0.0.0, Culture=neutral";
initParams.Reducer = "NosDB.Samples.MapReduceImplementation.ReducerFactory, NosDB.Samples.MapReduceImplementation, Version=1.0.0.0, Culture=neutral";
// Specify the output option, It will create the collection if it does not exist.
initParams.OutputOption = NosDB.Common.MapReduce.MROutputOption.CUSTOM_COLLECTION;
// You have to specify the custom collection name if the MROutputOption is set to CUSTOM_COLLECTION,
// For DEFAULT_COLLECTION, collection will be created as Collection_<Some_GUID>
initParams.CustomCollectionName = OUTPUT_COLLECTION_NAME;
// Specify the collections, on which you want to execute the map reduce task.
List <string> collections = new List <string>();
collections.Add("orders");
// The call which sends the task to the NosDB Server, and returns a trackable object.
// BEFORE EXECUTION:
// Make sure that you have deployed the implementation of mapreduce task (Mapper, Combiner and Reducer).
ITrackableTask trackableTask = _database.ExecuteTask(initParams, collections);
return(trackableTask);
}
/// <summary>
/// This method fetches the map reduce task result from the database and iterates the result
/// </summary>
/// <param name="trackableTask"> TrackableTask whos result will be fetched and iterated </param>
private void FetchAndReadTaskResult(ITrackableTask trackableTask)
{
// Call to get the result, this is a BLOCKING call... (it waits until task completes and returns the result...)
ITaskResult taskResult = trackableTask.GetResult();
//NOTE: There are other ways you can get the task result, Read more on the documentation...
IDBCollectionReader resultEnumerator = taskResult.GetEnumerator();
// Get and enumerate the result.
while (resultEnumerator.ReadNext())
{
//Reading the output
IJSONDocument document = resultEnumerator.GetDocument();
Console.WriteLine("Name: " + document["Key"] + " and Count available: " + document["Value"]);
}
// Now that we have gathered the data
// we can query the top results.
IDBCollectionReader rdr = _database.ExecuteReader("SELECT TOP 5 * FROM \"" + OUTPUT_COLLECTION_NAME + "\" ORDER BY Value DESC");
while (rdr.ReadNext())
{
//Reading the output
IJSONDocument document = rdr.GetDocument();
Console.WriteLine("Name: " + document["Key"] + " and Count available: " + document["Value"]);
}
}
/// <summary>
/// Executing this method will perform all the operations of the sample
/// </summary>
public void Run()
{
// Generate sample orders data to be used in this sample
ICollection <Order> orders = GenerateOrders();
// Initialize database and collection
InitializeDatabaseAndCollection();
// Insert some documents in the collection so that map reduce can run on it
InsertDocuments(orders);
// Execute map reduce task and get tracker
ITrackableTask trackableTask = ExecuteMapReduceTask();
// Fetch result and iterate the result
FetchAndReadTaskResult(trackableTask);
// Releasing the resources
_database.Dispose();
}
