Nested field support in Visualize

[Bargs]

Part of #1084

Similar to querying, aggregating on nested fields requires users to make some choices depending on what info seek. Imagine doing a terms aggregation on a nested field with a simple "count" metric. For each bucket, do you want to count the number of nested documents that match, or the number of parent documents? We can do either one and both might be useful depending on the question you're trying to answer. The Visualize editor will need to give the user a choice in a way that is easy to understand.

For non-count metrics that require selecting a specific field, I think we can handle things in a way that's transparent to the user. By selecting a field, you're already implicitly telling us whether to do the aggregation at the parent or child level.

Nested fields come along with two special aggregations for working with them, nested and reverse_nested. We'll need to use both to fully support nested fields in Visualize. Except in the case of the "count" metric (as mentioned above), we should be able to generate the necessary nested and reverse_nested wrappers using nested field information in the index pattern. I think the trickiest bit of the implementation will be keeping track of the current level of nesting as we generate the aggregation DSL, because we don't currently have a precedent in the visualize code for child aggs that know anything about their parents.

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[ppisljar]

Thank you for contributing to this issue, however, we are closing this issue due to inactivity as part of a backlog grooming effort. If you believe this feature/bug should still be considered, please reopen with a comment.

[a03nikki]

Considering the support for nested data type was started with #1084 and that ticket is in progress, it would be nice if it would include the visualizations as well. I would think this would be a sub-task of finishing #1084.

[elasticmachine]

Pinging @elastic/kibana-visualizations @elastic/kibana-visualizations-external (Team:Visualizations)

[dej611]

+1 https://discuss.elastic.co/t/kibana-visualize-lens-not-showing-nested-fields/322691

[jaGarcia]

+1 to supporting nested docs in Visualize

[sacalata]

+1 doesn't OpenSearch support this already?

[mgevans-5]

+1 we have some use cases for this feature too

[tom-allen]

+1 please reopen this. nested objects are very useful.

[shlomoksp]

+1

[Sagesh]

+1 Reopen this isssue

[gemo1011]

+1

[perceptivesecurity]

+1

[omar6995]

+20

[carlopuri]

+2*10^10000

[carlopuri]

digging with Vega with poor support isn't a good solution for visualise nested values...

[pvcasillasg]

+1

[ijardillier]

+1

[bosonno]

+1