About

SolrJs is a javascript client library that is topic of a 2008 google summer of code project. It is currently work in progress, this page is intended to show the project's status, some technical documentation and a collection of thoughts about future features. The current trunk is accessible at [http://solrstuff.org/svn/solrjs/trunk]

Architectural Overview

The library is written using the javascript toolkit jQuery [http://jquery.com/] (Version 1.2.5). SolrJS is included in one additional javascript file "solrjs.js" The idea is to create several (reusable and extensible) "widgets" that represent solr queries. A widget is a javascript object that is responsible for creating the according solr query as well as render the result from the server to html. One manager object acts as a container that holds these widgets, performs the actual query using jQueries getJSON [http://docs.jquery.com/Ajax/jQuery.getJSON#urldatacallback] method. This method creates a dynamic script tag, making cross-domain solr requests possible.

Examples and source code

The best way to get an idea how a widget may look like and how it can be integrated into html is to explore the documented source code and the test*.html example pages at [http://solrstuff.org/svn/solrjs/trunk].

Despite this, I'll try to describe some important implementation further on this page.

Implementation

Javascript matters

All SolrJS objects are created inside the jQuery.solrjs namspace. Given JQueries support for overriding the $() function, it is easily possible to use SolrJS alongside other javascript toolkits like prototype or custom javascript code.

Just include the following includes in the header section of your html:

<script src="jquery-1.2.5.js"/>
<script src="solrjs.js"/>
<script> var $sj = jQuery.noConflict(); </script> 

After that, all SolrJS objects are accessible using $sj.solrjs.*

The manager object

The manager object acts as "Controller" for the user input. It holds a state of the current solr query. The current query is represented by QueryItems objetcs. A query item simply is a field:value pair. A user may select or deselect multiple items. In the current work in progress, all query itemsa are concatinated using "AND" operators. More complex query generation may be implemented in the future. The manager currently provides the following methods:

How a query request works

Every widget implements a "getSolrUrl" method and performs its own http request. It also has to provide a "handleResult" method that gets the json data response to render. So if a user changes the selection:

Widget Inheritance

A main goal of the implementation was to create clean easy to understand code that can be easily extended by other developers. So I introduced a small OO inheritance pattern inspired by this thread [http://groups.google.com/group/jquery-dev/msg/12d01b62c2f30671] and created the factory method:

jQuery.solrjs.createClass = function(subClassName, baseClassName, subClass)

An "AbstractWidget" class is provided that acts as base class for all further widget implementations. In the source code, all methods that should be implemented by the child class are documented and marked as "abstract methods". An example syntax for a simple widget may be:

/*
 * Simple faceted view for one field.
 * 
 * @param "id": the widgetId
 * @param "target": the target html element in jquery notation
 * @param "fieldName": The facet field name
 */
jQuery.solrjs.createClass ("SimpleFacetWidget", "AbstractWidget", { 
  
  getSolrUrl : function(start) { 
    return "&facet=true&facet.field=" + this.fieldName;
  },

  handleResult : function(data) { 
    var values = data.facet_counts.facet_fields[this.fieldName];         
    jQuery(this.target).html("");
                
    for (var i = 0; i < values.length; i = i + 2) {
      var items =  "[new jQuery.solrjs.QueryItem({field:'" + this.fieldName + "',value:'" +  values[i] + "'})]";
      var label = values[i] + "(" + values[i+1] + ")";          
      jQuery('<a/>').html(label).attr("href","javascript:solrjsManager.selectItems('" + this.id + "'," + items + ")").appendTo(this.target);
        jQuery('<br/>').appendTo(this.target);
      }
  },

  handleSelect : function(data) { 
    jQuery(this.target).html(this.selectedItems[0].value);
    jQuery('<a/>').html("(x)").attr("href","javascript:solrjsManager.deselectItems('" + this.id + "')").appendTo(this.target);
  },

  handleDeselect : function(data) { 
    // do nothing
  }        
});

To add this widget to your html page, just create this script tag:

<script>
  var solrjsManager; 
  $sj(document).ready(function(){ 
    solrjsManager = new $sj.solrjs.Manager({solrUrl:"http://localhost:8983/solr/select"});   
    solrjsManager.addWidget(new $sj.solrjs.SimpleResultWidget({id:"result", target:"#result", rows:20}));       
    solrjsManager.addWidget(new $sj.solrjs.SimpleFacetWidget({id:"cat", target:"#cat", fieldName:"cat"}));
    solrjsManager.doRequestAll(); 
  });
</script>

Example for an easily customized widget: ExtensibleResultWidget

The ExtensibleResultWidget is a showcase of a flexible widget. It provides 2 abstract methods:

After the document result for the current page is returned, these methods are called and the user is able to use custom javascript code to render the result properly.

javascript:

var resultWidget = new $sj.solrjs.ExtensibleResultWidget({
  id:"result", 
  target:"#result", 
  rows:20,
  renderDataItem : function(item) { 
    jQuery('<div/>').html(item.id).appendTo(this.target);
    // more custom code for rendering one single result item
  }, 
  renderPageStatus : function(first, last, total) { 
    // custom code for rendering the pagination status                                  
    jQuery('#pageStatus_start').html(first + "");
    jQuery('#pageStatus_last').html(last + "");
    jQuery('#pageStatus_total').html(total + "");
    var navigation = $sj('#navigation').html("");
    var pageSize = last - first + 1;
    var lastpageFirst = Math.ceil(total / pageSize) * pageSize - pageSize;
    // create navigation buttons for paging
  }
});
solrjsManager.addWidget(resultWidget);          


html:

<body>
  <div id="pageStatus">
        Showing <span id="pageStatus_start"></span> to <span id="pageStatus_last"></span> of <span id="pageStatus_total"></span>
  </div>
  <div id="navigation"></div>
  <div id="result"></div>
</body>
        
                        

Ideas for future widgets

Feel free to extend this list.

Security concerns

As we have to access the solr web app directly to get the json data, a discussion about security was raised on the user list. See Ryan's posting about a single, restricted request handler that only allows selects (NO updates and deletes) [http://www.nabble.com/Announcement-of-Solr-Javascript-Client-to17462581.html#a17462581]. This "ProxyServlet" even could check and modify some parameters to avoid dos attacks or similar (eg. restricting &rows= to a reasonable maximum). Using the jQuery-getJSON method makes it possible to create cross site json requests, so we even can attach this restricted read-only url path to the solr webapp. Every user may then point the javascript client to eg.http://solrserver/readonly/