# Yahoo! UI Library

### datasource 3.1.1

Yahoo! UI Library > datasource > datasource-get.js (source view)
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    /**
     * Provides a DataSource implementation which can be used to retrieve data via the Get Utility.
     *
     * @module datasource
     * @submodule datasource-get
     */

    /**
     * Get Utility subclass for the DataSource Utility.
     * @class DataSource.Get
     * @extends DataSource.Local
     * @constructor
     */
    var DSGet = function() {
        DSGet.superclass.constructor.apply(this, arguments);
    };

    Y.DataSource.Get = Y.extend(DSGet, Y.DataSource.Local, {

    // Y.DataSouce.Get.prototype

        /**
         * Passes query string to Get Utility. Fires <code>response</code> event when
         * response is received asynchronously.
         *
         * @method _defRequestFn
         * @param e {Event.Facade} Event Facade with the following properties:
         * <dl>
         * <dt>tId (Number)</dt> <dd>Unique transaction ID.</dd>
         * <dt>request (Object)</dt> <dd>The request.</dd>
         * <dt>callback (Object)</dt> <dd>The callback object with the following properties:
         *     <dl>
         *         <dt>success (Function)</dt> <dd>Success handler.</dd>
         *         <dt>failure (Function)</dt> <dd>Failure handler.</dd>
         *     </dl>
         * </dd>
         * <dt>cfg (Object)</dt> <dd>Configuration object.</dd>
         * </dl>
         * @protected
         */
        _defRequestFn: function(e) {
            var uri  = this.get("source"),
                get  = this.get("get"),
                guid = Y.guid().replace(/\-/g, '_'),
                generateRequest = this.get( "generateRequestCallback" );

            /**
             * Stores the most recent request id for validation against stale
             * response handling.
             *
             * @property _last
             * @type {String}
             * @protected
             */
            this._last = guid;

            // Dynamically add handler function with a closure to the callback stack
            YUI.Env.DataSource.callbacks[guid] = Y.bind(function(response) {
                delete YUI.Env.DataSource.callbacks[guid];

                var process = this.get('asyncMode') !== "ignoreStaleResponses" ||
                              this._last === guid;

                if (process) {
                    this.fire("data", Y.mix({ data: response }, e));
                } else {
                    Y.log("DataSource ignored stale response for id " + e.tId + "(" + e.request + ")", "info", "datasource-get");
                }

            }, this);

            // Add the callback param to the request url
            uri += e.request + generateRequest.call( this, guid );

            Y.log("DataSource is querying URL " + uri, "info", "datasource-get");

            get.script(uri, {
                autopurge: true,
                // Works in Firefox only....
                onFailure: Y.bind(function(e) {
                    e.error = new Error("Script node data failure");
                    this.fire("error", e);
                }, this, e)
            });

            return e.tId;
        },

        /**
         * Default method for adding callback param to url.  See
         * generateRequestCallback attribute.
         *
         * @method _generateRequest
         * @param guid {String} unique identifier for callback function wrapper
         * @protected
         */
         _generateRequest: function (guid) {
            return "&" + this.get("scriptCallbackParam") +
                    "=YUI.Env.DataSource.callbacks." + guid;
        }

    }, {

    // Y.DataSouce.Get static properties

        /**
         * Class name.
         *
         * @property NAME
         * @type String
         * @static
         * @final
         * @value "dataSourceGet"
         */
        NAME: "dataSourceGet",

        ////////////////////////////////////////////////////////////////////////////
        //
        // DataSource.Get Attributes
        //
        ////////////////////////////////////////////////////////////////////////////
        ATTRS: {
            /**
             * Pointer to Get Utility.
             *
             * @attribute get
             * @type Y.Get
             * @default Y.Get
             */
            get: {
                value: Y.Get,
                cloneDefaultValue: false
            },

            /**
             * Defines request/response management in the following manner:
             * <dl>
             *     <!--<dt>queueRequests</dt>
             *     <dd>If a request is already in progress, wait until response is
             *     returned before sending the next request.</dd>
             *     <dt>cancelStaleRequests</dt>
             *     <dd>If a request is already in progress, cancel it before
             *     sending the next request.</dd>-->
             *     <dt>ignoreStaleResponses</dt>
             *     <dd>Send all requests, but handle only the response for the most
             *     recently sent request.</dd>
             *     <dt>allowAll</dt>
             *     <dd>Send all requests and handle all responses.</dd>
             * </dl>
             *
             * @attribute asyncMode
             * @type String
             * @default "allowAll"
             */
            asyncMode: {
                value: "allowAll"
            },

            /**
             * Callback string parameter name sent to the remote script. By default,
             * requests are sent to
             * &#60;URI&#62;?&#60;scriptCallbackParam&#62;=callbackFunction
             *
             * @attribute scriptCallbackParam
             * @type String
             * @default "callback"
             */
            scriptCallbackParam : {
                value: "callback"
            },

            /**
             * Accepts the DataSource instance and a callback ID, and returns a callback
             * param/value string that gets appended to the script URI. Implementers
             * can customize this string to match their server's query syntax.
             *
             * @attribute generateRequestCallback
             * @type Function
             */
            generateRequestCallback : {
                value: function () {
                    return this._generateRequest.apply(this, arguments);
                }
            }
        }
    });

    YUI.namespace("Env.DataSource.callbacks");

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