CosmosDB's index recommendations that include arrays seem to be in an unsupported format (w/ PopulateIndexMetrics)

Author: Dan

Originally Sourced from: https://stackoverflow.com/questions/75203887/cosmosdbs-index-recommendations-that-include-arrays-seem-to-be-in-an-unsupporte

I'm using CosmosDB's V3 API. I set PopulateIndexMetrics to true to generate index recommendations. However, some of the recommendations (relating to arrays) seem to be in an unsupported format and when I try and add them as is (to my containers' indexes) the operation fails.

Here is an example composite index recommendation which I get when I set PopulateIndexMetrics to true (where a and c are simple string properties and b is an array of strings):

Index Spec: "/a ASC, /b/[] ASC, /c ASC\r\n"

However, this array format isn't supported when I try and add this composite index via the Azure Portal. And I've already added this to the index: "/a ASC, /b ASC, /c ASC" (I removed the square parantheses) yet when I rerun the index recommender it still re-recommends the missing index with the unsupported format.

Any help would be appreciated.

Thanks!