Querying Solr using a pure AJAX application

This is the third (and final) post related to the GBIF Metacatalogue Project. The first 2 were dedicated to explain how the data is harvested and how that information is stored in Apache Solr. Those post can be consulted in:

• OAI-PMH Harvesting at GBIF
• Indexing bio-diversity metadata using Solr: schema, import-handlers, custom-transformers

One the nicest features of Solr is that most of its functionalities are exposed via Rest API. This API can be used for different operations like: delete documents, post new documents and more important to query the index. In cases when the index is self-contained (i.e: doesn't depend of external services or storages to return valuable information) a very thin application client without any mediator is viable option. In general terms, "mediator" is a layer that handles the communication between the user interface and Solr, in some cases (possibly) that layer manipulates the information before send it to user interface. Metadata Web application is a perfect example of the scenario just described: it's basically an independent storage of documents that can be used to provide free and structured search. All the information is collected from several sources and then is store in the Solr index, even the full XML documents are stored in the Solr Index. AJAX Solr is a Javascript framework that facilitates querying a Solr server and the display of results in a Web Application; to implement the remote communication only requires a way of sending requests to Solr, in our case, we used JQuery. In AJAX Solr the information is displayed to the end-user by widgets like: facets widgets, list of results, cloud widgets, etc. Widgets

Widgets

In this context widgets are user interface componenents whose functionality doesn't depend on other widgets, each one has an specific responsabilty. All the communication (between Solr and the UI) is handled by Manager whose main responsability is send the requests and communicates the responses to the widgets. The image below shows some widgets examples: From the implementation point of view the code below shows how the manager is created and the way of attach widgets to it:

$(function () {
  Manager = new AjaxSolr.Manager({
    solrUrl: solrServerUrl
  });
  /*Adds a listener widgets to the Manager*/
  Manager.addWidget(new AjaxSolr.ResultWidget({
    id: 'result',
    target: '#docs' //<-- element where the result will be displayed     }));
 Manager.addWidget(new AjaxSolr.PagerWidget({    
     id: 'pager',    
     target: '#pager',    
     prevLabel: '<',    
     nextLabel: '>... 

Then, we "simply" add the desired params to perform the query:

  Manager.store.addByValue('facet.field', 'providerExact');
  Manager.store.addByValue('facet.date', 'endDate');
  Manager.store.addByValue('q', '*:*');
  Manager.doRequest();

Other libraries

Some other components were used in order to provide a better user experience, those are:

• JQuery/JQuery UI (http://jquery.com/): AJAX Solr requires a library to implement the AJAX requests. JQuery was chosen for this purpose. Additionally, several JQueryUI widgets are extensively used for a richer user experience.
• SyntaxHighlighter(http://alexgorbatchev.com/SyntaxHighlighter/): this is a code syntax highlighter developed in JavaScript, This component is used for displaying the XML view of a metadata document.

The prototype application is available here; this application is 99.9% free of server-side code, there's only one line of code with server dependency, and is for indicate the Solr server url:

var solrServerUrl = <%="'" + config.getServletContext().getInitParameter("solrServerUrl") + "'"%>;

However, that line can be modified easily to deploy the same application in other web server technology rather than a Servlet container (Tomcat, Jetty, etc.).