# Custom aggregation plugin with multiple result reader

**URL:** <https://discuss.elastic.co/t/custom-aggregation-plugin-with-multiple-result-reader/234425>\
**Category:** Elasticsearch\
**Created:** [May 26, 2020, 9:51pm UTC](https://discuss.elastic.co/t/custom-aggregation-plugin-with-multiple-result-reader/234425 "2020-05-26T21:51:28Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![sylvain.mazet](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@sylvain.mazet](https://discuss.elastic.co/u/sylvain.mazet)\
**Post date:** [May 26, 2020, 9:51pm UTC](https://discuss.elastic.co/t/custom-aggregation-plugin-with-multiple-result-reader/234425/1 "2020-05-26T21:51:28Z")

</div>

Hi all.  
I am writing a specific aggregation plugin (not the first one I write...)  
for ES version 6.6.

This plugin can compute various aggregations (intended for process mining) on the data,  
with only one aggregation builder class on input. (We make these computation in a plugin for performance reasons).

My issue is the return type of the aggregation query.  
**I would like the return type to depend on the aggregation query configuration parameters**.

```
{...,
     "aggs" : { "first" : {"my_custom_aggregation": {"algorithm" : "firstAlgorithm"}},
                "second": {"my_custom_aggregation": {"algorithm" : "secondAlgorithm"}},
                 "third": {"my_custom_aggregation": {"algorithm" : "thirdAlgorithm"}},
     }
 }

```

For the first algorithm, I return a list of things (so-called "processes") in a  
`class FirstAlgorithmInternalAggregation extends InternalAggregation`,  
I do not even need buckets in this case.

For the second algorithm, I return a true list of buckets in a  
`class SecondAlgorithmInternalAggregation extends InternalMultiBucketAggregation`

For the third algorithm, I return a true list of buckets in a  
`class ThirdAlgorithmInternalAggregation extends InternalMultiBucketAggregation`

The buckets in these results are enriched with various information, that vary with the algorithm used.

When I query and get the response through a python script (using python module "elasticsearch"), the answers come back in python dictionaries, and I can parse them, extract the results, etc...  
I am guessing the python module goes through the REST API and that the JSON serialization deals with the various result types.

When I query through Java API, I have a problem: from what I understand the serialization of the answer must be known and declared at plugin registration time in the

```auto
List<AggregationSpec> getAggregations() {...}

```

method of the `MyCustomPlugin` class.  
Right now, I register only one `AggregationSpec`, with one result reader there, which reads only one type of `InternalAggregation`.

**I am seeking to build and return different "InternalAggregation"'s in the response, depending on the plugin parameters.**

So my questions:

1. Is it even possible to return objects of different types through the Java API, based only on the builder parameters?
2. If I return more than one AggregationSpec from `getAggregations`, what are the semantics?
3. Could I design a result reader that would be able to deserialize various return types? Not sure this is possible.

I could probably unify the return types, but they are quite different. I would like to avoid it.

I could also separate the entry points for the three algorithms, but it would be nice to avoid creating a different entry point for each algorithm (the computation machineries have a lot in common under the hood).

Any help appreciated.  
Thanks for reading!

Sylvain Mazet.

---

<div class="post-metadata">

**Author:** ![sylvain.mazet](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@sylvain.mazet](https://discuss.elastic.co/u/sylvain.mazet)\
**Post date:** [May 28, 2020, 4:03pm UTC](https://discuss.elastic.co/t/custom-aggregation-plugin-with-multiple-result-reader/234425/2 "2020-05-28T16:03:55Z")

</div>

Partially answering myself here.

I opted for multiple entry points,  
and partially answered question 2:  
returning multiple AggregationSpec allows me to register  
more than one builders.

(Partially because I still don't know what happens if I register more than one ResultReader  
per AggregationSpec).

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [June 25, 2020, 4:04pm UTC](https://discuss.elastic.co/t/custom-aggregation-plugin-with-multiple-result-reader/234425/3 "2020-06-25T16:04:00Z")

</div>

Closed on June 25, 2020, 4:04pm UTC

This topic was automatically closed 28 days after the last reply. New replies are no longer allowed.