The AJAX Solr architecture

The Manager controller performs a two-way communication with our Solr server. It accepts solrUrl or proxyUrl as its parameter. SolrUrl is used when Manager communicates with Solr directly. ProxyUrl is used when it interacts with Solr through a proxy. Ideally, we would not like to expose our Solr server to the Internet, so we can put it behind a proxy server and specify ProxyUrl in the Manager. The proxy server can also be configured to prevent Denial of Service (DoS) attacks and ensure the number of records in the result set is at a maximum (by restricting the row parameter).

The solrUrl parameter should hold the absolute URL of the Solr application and can be represented using the following code snippet:

Manager = new AjaxSolr.Manager({   solrUrl: "http://127.0.0.1:8983/solr/" });

In our case, the Solr server is on the local machine, so we have specified the local machine's IP address.

In the implementation of the solrUrl parameter, AJAX Solr uses the select servlet by default. If you want to change the default value of the servlet parameter, you need to pass the servlet parameter to Manager at the time of initialization, as shown in the following code snippet:

Manager = new AjaxSolr.Manager({   solrUrl: 'http://127.0.0.1:8983/solr/',   servlet: 'readonly' });

The Manager life cycle can be represented using the following image that shows how the different components of AJAX Solr interact with each other.

The ParameterStore object can be attached to Manager by the setStore method, as shown in the following snippet:

Manager.setStore(new AjaxSolr.ParameterStore());

Similarly, the widgets to be used for display can be attached to Manager by using the addWidget method, as shown in the following snippet:

Manager.addWidget(new AjaxSolr.AbstractWidget({   id: 'identifier',   target: '#css-selector' }));

Once parameterStore and widgets are attached to Manager, we can call the init method of the Manager to initialize AJAX Solr. This in turn calls the init methods of the attached components, ParameterStore and widgets.

Manager.init();

Once Manager is initialized, we can call the doRequest() method to send the first request to Solr:

Manager.doRequest();

If any widget wishes to perform an action prior to sending the request to Solr (for instance, displaying throbber gif image), doRequest triggers the beforeRequest method of each of the widgets. The throbber may include activities such as content download, computation of some values, or interaction with an external device. Then, the executeRequest abstract method is called that actually sends the request to Solr. The AJAX implementation of Solr is JavaScript framework agnostic. Any framework supporting AJAX implementation can be used to send the AJAX request to Solr. This is handled by the Manager.jquery.js file, which resides in the managers folder inside the ajax-solr library. This implements the executeRequest method using jQuery. As soon as the Manager receives a response from Solr, it captures the JSON response in its response property. It then triggers the afterRequest method of each widget so that the response property is investigated by the widgets and rendered to the interface accordingly.

The parameterStore model is used to store Solr parameters. It defines functions for fetching, setting, and removing Solr parameters. Some Solr parameters, such as facet.field and fq, may be specified multiple times. Other parameters, such as q and start, may be specified only once. There is the isMultiple method, which returns true if the parameter can be specified multiple times.

There is a list of functions that operate on Solr parameters, and their behavior is based on whether a specific parameter needs to be used multiple times or just once. These functions can be categorized as follows:

Let us understand these categories.

<script type="text/javascript" src="ajax- solr/core/ParameterHashStore.js"></script>

Manager.setStore(new AjaxSolr.ParameterHashStore());

Manager.store.exposed = [ 'fq', 'q', 'start' ];

The purpose of widgets is to inspect the JSON response retrieved from Solr by Manager and update the interface accordingly. AbstractWidget is the base class from which all widgets are inherited. Each widget accepts two parameters:

The AbstractWidget base class exposes three abstract methods:

AJAX Solr defines a set of abstract widgets that we can use to write our own widgets. In order to benefit from the functions that are contained in these widgets, we just need to write a new widget that inherits one of the following widgets: