HOAB

Problem :

I try to create an aggregation (count and groupBy) on my documents.

Thanks to these links :

• Stackoverflow1
• Baeldung projection & aggregation

I nearly resolve my problem... nearly :)

Solution :

Documents to analyze :

1. the _id of the application is defined by an id attribute...
2. instance is not present is all documents

{
   phase : "Production",
   application {
      _id : 1234
   },
   instance: "myInstance"
}

The first try is to use springdata easy way : there is not groupBy ! but count is working if you need :

# If instance is set to null, returns the document which do not have the field
countByApplicationIdAndPhaseAndInstanceId(Long applicationId, Phase phase, String instance)

# Another way to test instance presence
countByApplicationIdAndPhaseAndInstanceIdExists(Long applicationId, Phase phase, Boolean exists)

So, thanks to baeldung (many thanks) ! Here is a working solution, take care about :

1. filtering order ! the Match operation works either on the document, either on the result of the group by ! (see Baeldung example for testing result of the group by)

#Filter on document
        Aggregation aggregation = newAggregation(filterStates, agg);

#Filter on result of the aggregation
        Aggregation aggregation = newAggregation(agg, filterStates);

1. my applicationId as used in Springdata easy way must be written with Mongo ID : application._id
2. and application_id could not be present in the group clause as it is filtered (but as it takes me 2 long hours to make it works....)
3. Don't forget @Id on the result bean. I see somewhere that we can execute the generic command in Mongo and do not take care about the result bean.
4. The @Id must be on the first item of the group
5. Do not miss the collection name in the aggregation command (here MONGO_EVALUATION_COLLECTION_NAME)

@Service
public class EvaluationAdditionalRepository {

    private static final Logger LOGGER = LoggerFactory.getLogger(EvaluationAdditionalRepository.class);

    @Autowired
    private MongoTemplate mongoTemplate;


    public List<InstanceCount> getInstanceByApplicationAndPhase(Long applicationId) {

        GroupOperation agg = group("application._id", "instanceId", "phase").count().as("countInstance");
        MatchOperation filterStates = match(new Criteria("application._id").is(applicationId));

        Aggregation aggregation = newAggregation(filterStates, agg);
        AggregationResults<InstanceCount> result = mongoTemplate.aggregate(aggregation, MONGO_EVALUATION_COLLECTION_NAME, InstanceCount.class);

        return result.getMappedResults();
    }
}

And the result bean :

import org.springframework.data.annotation.Id;

public class InstanceCount {

    @Id
    private Long applicationId;

    // Enum are authorized
    private Phase phase;

    private long countInstance;

    private String instanceId;

    public Phase getPhase() {
        return phase;
    }

    public void setPhase(Phase phase) {
        this.phase = phase;
    }

    public long getCountInstance() {
        return countInstance;
    }

    public void setCountInstance(long countInstance) {
        this.countInstance = countInstance;
    }

    public Long getApplicationId() {
        return applicationId;
    }

    public void setApplicationId(Long applicationId) {
        this.applicationId = applicationId;
    }

    public String getInstanceId() {
        return instanceId;
    }

    public void setInstanceId(String instanceId) {
        this.instanceId = instanceId;
    }

    @Override
    public String toString() {
        return "InstanceCount{" +
            ", applicationId='" + applicationId + '\'' +
            ", phase='" + phase + '\'' +
            ", instanceId='" + instanceId + '\'' +
            ", countInstance=" + countInstance +
            '}';
    }
}