if there is no data "getUniqueMappedResult" throws an exception

[blueiceprj]

Hello,

If you add a new function with Optional value return its would be useful to control return value.

Current Implementation and throw an exception if there is no data

	@Nullable
	public T getUniqueMappedResult() {
		Assert.isTrue(mappedResults.size() < 2, "Expected unique result or null, but got more than one!");
		return mappedResults.size() == 1 ? mappedResults.get(0) : null;
	}

Optional<T> ..... Thanks

[christophstrobl]

Please spend a bit more time describing your request (maybe outline the usage scenario you have in mind). Right now, we struggle to understand what you want to achieve.

[blueiceprj]

Hi, Ok. I try to explain on my case and solution.

	public StudentAttendanceDTO getAttendance(StudentAttendanceSearchDTO dto)
	{
		final List<AggregationOperation> pipeline =new ArrayList<>();
		pipeline.add(Aggregation.group("info.studentId").count().as("courseEventsPlanned") 
				.sum(ConditionalOperators.Cond.when(Criteria.where("info.type").is(AttendanceType.PRESENT)).then(1).otherwise(0))
				.as("courseEventsAttended")
				..................
                                ...................................
                final AggregationResults<R> aggregate = template.aggregate(pipeline, collectionName, outputClass);
		return uniqueResult(collectionName, AttendanceDTO.class,
				Aggregation.newAggregation(pipeline));
	}

       // I have to use this method to return without exception. This my solution
       private <R> R getUniqueResult(final AggregationResults<R> aggregate)
	{
		List<R> results = aggregate.getMappedResults();
		if (isNotEmpty(results))
		{
			return results.get(0);
		} else
		{
			return null;
		}
	}

       // If I need optional version I use this
       protected <R> Optional<R> getUniqueResultOf(final AggregationResults<R> aggregate)
	{
		List<R> results = aggregate.getMappedResults();
		if (isNotEmpty(results))
		{
			return Optional.of(results.get(0));
		} else
		{
			return Optional.empty();
		}
	}

instead of this implementation

       public Optional<StudentAttendanceDTO> getAttendance(StudentAttendanceSearchDTO dto)
	{
		final List<AggregationOperation> pipeline =new ArrayList<>();
		pipeline.add(Aggregation.group("info.studentId").count().as("courseEventsPlanned") 
				.sum(ConditionalOperators.Cond.when(Criteria.where("info.type").is(AttendanceType.PRESENT)).then(1).otherwise(0))
				.as("courseEventsAttended")
				..................
                                ...................................
                final AggregationResults<R> aggregate = template.aggregate(pipeline, collectionName, outputClass);
               // It throws an exception if there is no data 
		return aggregate.getUniqueMappedResult();
             // It would be very useful if you add to new version of this method like this
               return aggregate.getUniqueMappedResultOf(); // optional and return object as Optional<StudentAttendanceDTO>
	}

[christophstrobl]

Sorry for long silence. We've been revisiting the issue and will not add an additional method returning Optional<T> to AggregationResults. Optional.ofNullable(result.getUniqueMappedResult()) should be sufficient to support the described use case.