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MapReduce Views Using the Java SDK with Couchbase Server

You can use MapReduce views to create queryable indexes in Couchbase Server.

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Querying Views

View operations are accessible on the Bucket API. Once you have a reference to the bucket you need to at least supply the name of the design document and the name of the view:

ViewResult viewResult = bucket.viewQuery("dev_landmarks-by-name", "by_name");
for (ViewRow row : viewResult.rows()) {
  System.out.println("Found row: " + row);
}

It is important to remember that by default, the SDK will look for a view deployed to the production namespace. If you want to query one which is still in the development namespace you can do it like this:

ViewResult viewResult = bucket.viewQuery("landmarks-by-name", "by_name",
    viewOptions().namespace(DesignDocumentNamespace.DEVELOPMENT));

In the same way you can supply all kinds of different options, including the ViewScanConsistency which was previously called Stale.

ViewResult viewResult = bucket.viewQuery("dev_landmarks-by-name", "by_name",
    viewOptions().scanConsistency(ViewScanConsistency.REQUEST_PLUS).limit(5).inclusiveEnd(true));

If you have a reduce function in your view and you want to call it, make sure to call .reduce(true) as well.

Working with View Rows

A ViewResult can emit 0 to N view rows. The available data inside each ViewRow depends both on the map function written and if a reduce function is used.

The structure of a ViewRow looks like this:

public class ViewRowExample {

  public Optional<String> id() {
    Optional<String> result = null;
    /*  */ return result;
  }

  public <T> Optional<T> keyAs(Class<T> target) {
    Optional<T> result = null;
    /*  */ return result;
  }

  public <T> Optional<T> keyAs(TypeRef<T> target) {
    Optional<T> result = null;
    /*  */ return result;
  }

  public <T> Optional<T> valueAs(Class<T> target) {
    Optional<T> result = null;
    /*  */ return result;
  }

  public <T> Optional<T> valueAs(TypeRef<T> target) {
    Optional<T> result = null;
    /*  */ return result;
  }
}

Both the key and the value can be converted into any target type, depending on how you wrote your view function. Note that the document ID is always a String, but it is wrapped in an Optional because it is not available if a reduce function is used.

Accessing View Metadata

In addition to the rows the view result contains additional ViewMetaData.

ViewResult viewResult = bucket.viewQuery("dev_landmarks-by-name", "by_name", viewOptions().debug(true));

ViewMetaData viewMeta = viewResult.metaData();
System.out.println("Got total rows: " + viewMeta.totalRows());
viewMeta.debug().ifPresent(debug -> System.out.println("Got debug info as well: " + debug));

The number of rows is always present, the debug information only if you enable it on the ViewOptions as indicated through being wrapped into an Optional<JsonObject>.