BackendService.lzx

<library>

  <!---
         BackendService: Class connecting to a REST webservice and handling success
                   of failure of the service call.

         Usage:
         @START_CODE
         <canvas>
      <dataset name="i18nDS" src="http:labs.openlaszlo.org/lzproject/lzproject/rest/application/i18n" type="http" request="true" proxied="true" />
      <BackendService name="i18n"
        successDatapath="i18nDS:/app/currentLocale">
        <handler name="ontrigger" args="obj">
          this.prepareParams(obj.collectValues());
        </handler>
        <method name="handleError">
          Debug.write('Error requesting application resource bundle (i18n)!');
        </method>
        <method name="handleSuccess" args="msg, p">
          Debug.write('Resource bundle loaded');
          // If we are already logged in, we have to reload the data
          // containing I18N strings
          if (canvas.loggedIn) {
            canvas.services.listTasks.startRequest();
            canvas.services.listProjects.startRequest();
            canvas.services.listUsers.startRequest();
          }
        </method>
      </BackendService>
         </canvas>
         @END
    -->
  <class name="BackendService" extends="node">
        <!-- PUBLIC ATTRIBUTE SECTION -->
        <!--- The xpath which has to match for a successful request -->
    <attribute name="successDatapath" type="string" value=""/>
    <!--- The xpath singalling a request error -->
    <attribute name="failureDatapath" type="string" value=""/>
    <!--- Used as an event sender by the ServiceConnectors connecting to this service -->
    <attribute name="trigger" type="number" value="0"/>
    <!--- If we display an error message in a form we fwant to be able to clear that
         message after a certain time. This is the delegate used for the timer -->
    <attribute name="clearMessageDel" type="expression" value="null"/>
    <!--- How much time should we wait before removing the error message. Of course this
         value can be overriden in any instance -->
    <attribute name="clearDelay" type="number" value="2500"/>
    <!--- HTTP method: POST or GET -->
    <attribute name="httpMethod" type="string" value="GET"/>

        <!-- PRIVATE ATTRIBUTE SECTION -->
    <!--- @keywords private Reference to a service connector. Is set by from within
          the ServiceConnector class -->
    <attribute name="_connector" type="expression" value="null"/>
        <!--- @keywords private Reference to the dataset used by this service -->
    <attribute name="_dsRef" type="expression" value="null"/>
        <!--- @keywords last message returned by webservice -->
    <attribute name="_errorCount" type="number" value="0"/>
        <!--- @keywords last message returned by webservice -->
    <attribute name="_lastMessage" type="string" value=""/>
        <!--- @keywords timestamp for last request -->
    <attribute name="_lastRequestTime" type="expression" value="null"/>
        <!--- @keywords counting the total number of request for this service -->
    <attribute name="_requestCount" type="number" value="0"/>
        <!--- @keywords counting the total number of request for this service -->
    <attribute name="_xmlSerialized" type="string" value="no XML document received yet"/>

    <!-- Service state constants -->
    <attribute name="IDLE" type="string" value="idle"/>
    <attribute name="REQUEST_STARTED" type="string" value="request started"/>
    <attribute name="PROCESSING_RESPONSE" type="string" value="processing response"/>
    <attribute name="WAITING_FOR_CLEAR" type="string" value="idle"/>


    <!-- DATAPOINTERS -->
    <!-- Datapointer for catching a success -->
    <datapointer name="_successDP" rerunxpath="true">
      <handler name="ondata" args="p">
           if (p !=null) {
             var dupe = this.dupePointer();
             dupe.setXPath("/");
             classroot._xmlSerialized = dupe.serialize();
           classroot._lastMessage = this.getNodeText();
           classroot.handleSuccess(this.getNodeText(), p);
          classroot.setupTimer();
          classroot.ondata.sendEvent();
          }
      </handler>
      <handler name="onerror" args="err">
        classroot._errorCount++;
          classroot.handleError();
      </handler>
      <handler name="ontimeout" args="e">
        Debug.error(e);
        Debug.error('Timeout for REST webservice ' + this.name);
      </handler>

    </datapointer>

    <!-- Datapointer for catching an erraneous service request -->
    <datapointer name="_failureDP" rerunxpath="true">
      <handler name="ondata" args="p">
         if (p !=null) {
             var dupe = this.dupePointer();
             dupe.setXPath("/");
             classroot._xmlSerialized = dupe.serialize();
           classroot._lastMessage = this.getNodeText();
          classroot.handleFailure(this.getNodeText());
          classroot.setupTimer();
          classroot.ondata.sendEvent();
        }
        </handler>

    </datapointer>

        <!-- EVENT & HANDLER SECTION -->
        <!-- Event for the trigger starting a service request -->
    <event name="ontrigger"/>
    <event name="ondata"/>

    <!-- Constructor -->
    <handler name="onconstruct">
      if (typeof(canvas.services) == 'undefined') {
          canvas.services = new Array();
      }
    </handler>


    <!-- METHOD SECTION -->
      <!--- set the timer which will call the clear() method after an error
            message has been displayed. -->
    <method name="setupTimer">
      if (typeof this.clearMessage == 'function') {
        if (this.clearMessageDel == null) {
          this.clearMessageDel = new LzDelegate( this, "clearMessage" );
        } else {
          this.clearMessageDel.unregisterAll();
        }
        lz.Timer.addTimer( this.clearMessageDel, this.clearDelay);
      }
    </method>

        <!-- METHOD SECTION -->
        <!--- init method  -->
        <method name="init">
      super.init();
      _successDP.setAttribute('xpath', this.successDatapath);
      // While the succuss datapath is is a requirement, the
      // failure datapath is optional.
      if (this.failureDatapath != null) {
          _failureDP.setAttribute('xpath', this.failureDatapath);
      }
      this._dsRef = canvas[this.name+'DS'];
      // Push this service object to the canvas.services array
      canvas.services[this.name] =  this;
    </method>

      <!--- Turn the associative array returned by the form into params for
            an HTTP reqeust.
            @param array values: An associative array containing the values
                                 passed to the service -->
       <method name="prepareParams" args="values">
      for (var key in values) {
          Debug.write('Adding var ' + key + '=' + values[key] + ' to params');
          this._dsRef.setQueryParam(key, values[key]);
      }
      this.startRequest();
    </method>

    <method name="handleError">
      Debug.error("Error calling REST web service " + this.name);
    </method>

    <!--- Start the request to the REST webservice -->
    <method name="startRequest">
      this._lastRequestTime = new Date();
      this._requestCount++;
      this._dsRef.setAttribute('querytype', this.httpMethod);
      this._dsRef.doRequest();
    </method>

  </class>

</library>
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