Background
ElasticGraph's sourced_from feature lets a field on an indexed type be populated from a different source type's events, rather than from the indexed type's own events. #1252 extended this so a sourced_from field can live on a nested element of an indexed document, not just at the top level of the document.
Separately, ElasticGraph maintains a hidden __counts map on indexed documents to track the sizes of list fields. When a list field's contents change, ElasticGraph recomputes its count so that list-size-based queries stay correct.
Feature gap
Nested sourced_from currently supports sourcing scalar and object fields onto a nested element, but not list fields. In order to support sourcing nested list fields, the __counts tracking must work for these fields (there is currently no mechanism for this for the nested sourced field case).
Interim state
Until this is supported, a schema-dump-time validation will reject defining such a schema with a clear error pointing to this issue.
Background
ElasticGraph's
sourced_fromfeature lets a field on an indexed type be populated from a different source type's events, rather than from the indexed type's own events. #1252 extended this so asourced_fromfield can live on a nested element of an indexed document, not just at the top level of the document.Separately, ElasticGraph maintains a hidden
__countsmap on indexed documents to track the sizes of list fields. When a list field's contents change, ElasticGraph recomputes its count so that list-size-based queries stay correct.Feature gap
Nested
sourced_fromcurrently supports sourcing scalar and object fields onto a nested element, but not list fields. In order to support sourcing nested list fields, the__countstracking must work for these fields (there is currently no mechanism for this for the nested sourced field case).Interim state
Until this is supported, a schema-dump-time validation will reject defining such a schema with a clear error pointing to this issue.