views.md

Finding documents with views

Use views to index or summarise your data so that you can find what you need. The CouchDB database has a good guide to views, read that first then follow the rest of this document to see how to use them from Clojure.

Create your views

Use the admin page on your database, often here: http://127.0.0.1:5984/_utils/ to create a new view.

Select your database, then click the 'View' dropdown, then 'Temporary View...', this opens up a split pane JavaScript editor, with space for a 'map' function on the left and a 'reduce' function on the right.

Here's an example that produces a map from tags to document ids:

function(doc) {
  if ('tags' in doc) {
    doc.tags.forEach( function(tag) {
      emit(tag, doc._id );
    });
  }
}

Make sure you name and save your temporary view. As a guide, the design document can be named by the entity (in this case 'pages') and the view by the key (in this case 'by_tag').

Calling views from your code

Once you've created, tested and saved your new view, call it using get-view:

> (with-db (couch/get-view "pages" "by_tag" {:key "tag1"}))
({:id "a-new-page", :key "tag1", :value "a-new-page"}
 {:id "a-new-page-2", :key "tag1", :value "a-new-page-2"})

As you can see, get-view returns a list of hash-maps that identify the matching documents.