How to get ordered results from couchbase

Question

I have in my bucket a document containing a list of ID (childList). I would like to query over this list and keep the result ordered like in my JSON. My query is like (using java SDK) :

String query = new StringBuilder().append("SELECT B.name, META(B).id as id ") .append("FROM" + bucket.name() + "A ") .append("USE KEYS $id ") .append("JOIN" + bucket.name() + "B ON KEYS ARRAY i FOR i IN A.childList end;").toString();

This query will return rows that I will transform into my domain object and create a list like this :

n1qlQueryResult.allRows().forEach(n1qlQueryRow -> (add to return list ) ...);

The problem is the output order is important.

Any ideas?

Thank you.

Answer 1

here is a rough idea of a solution without N1QL, provided you always start from a single A document:

List<JsonDocument> listOfBs = bucket
      .async()
      .get(idOfA)
      .flatMap(doc -> Observable.from(doc.content().getArray("childList"))) 
      .concatMapEager(id -> bucket.async().get(id))
      .toList()
      .toBlocking().first();

You might want another map before the toList to extract the name and id, or to perform your domain object transformation even maybe...

The steps are:

1. use the async API
2. get the A document
3. extract the list of children and stream these ids
4. asynchronously fetch each child document and stream them but keeping them in original order
5. collect all into a List<JsonDocument>
6. block until the list is ready and return that List.