azure - CosmosDB - Correct Partition Key

Question

Every JSON file I upload to the collection is in the following format:

{
  "Blocks": [
    {
      "radarID": "51p01", ...
    },
    {
      "radarID": "51p02", ...
    }
  ]
}

The partition key I use is '/Blocks/radarID', but it does not work. I guess radarID is not an immediate child of Blocks, it is in a list. So do you know what I should write as my partition key?

Thanks.

Answer 1

Partition Key has to be a single value for each document, it can't be a field in sub-array. Partition Key is used to determine which database node will host your document, and it wouldn't be possible if you specified multiple values, of course.

If your single document contains data from multiple entities, and you will query those entities separately, it might make sense to split your documents per entity. If all those "radars" are related to some higher level entity, use that entity ID as partition key.

Bottom line: partition key should be defined by your query patterns, so that the most popular queries are executed against a single partition.