CouchDB: Return Newest Documents of Type Based on Timestamp

Question

I have a system that accepts status updates from a variety of unique sources, and each status update creates a new document in the following structure:

{
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Answer 1

You can get the latest timestamp for every source using the _stats built-in reduce function, then do another query to get the documents. Here's the views:

"views": {
  "latest_update": {
    "map": "function(doc) { if (doc.type == 'status_update') emit(doc.source_id, doc.timestamp); }",
    "reduce": "_stats"
  },
  "status_update": {
    "map": "function(doc) { if (doc.type == 'status_update') emit([doc.source_id, doc.timestamp], 1); }"
  }
}

First query latest_update with group=true, then status_update with something like (properly url-encoded):

keys=[["truck123",TS123],["truck234",TS234],...]&include_docs=true

where TS123, and TS234 are the values of max returned by latest_update.