Support nested aggregation

[n1k0]

I'm trying to aggregate distinct values for some nested property value:

{
  "aggs" : {
    "source_repos" : {
      "terms": {
        "field" : "source.tree",
        "size" : 1000
      }
    }
  }
}

Running this query, I get an empty object (but I think there's an issue about this already), and this error in the server logs:

Fielddata is disabled on text fields by default. Set fielddata=true on [source.tree] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead.

I'm no expert in ES, so I don't have any idea how I can do what is suggested here; thoughts?

[leplatrem]

That may be related to #8

[leplatrem]

Ok I investigated a bit more about this.

By default ES infers types from data.

Doing aggregations for distinct values is very costly for text fields. In our case, our fields are more keywords values (like enums) than proper (full)text.

While fixing #8, we'll have to provide a way to specify the index (index:schema field on the collection metadata, like ui:schema) and we'll be able to specify our mapping types manually.

I close in favor of #8