Creating REST Services and Clients with Ensemble
Developing a REST Operation
[Back] [Next]

To develop a REST operation, you extend the class EnsLib.REST.Operation. The REST operation uses Ensemble’s outbound HTTP adapter, which is described in Using the HTTP Outbound Adapter.

Using the HTTP Outbound Adapter, you specify the server, port, and address of the external web service in the HTTP adapter configuration. For example, to define a REST operation that calls a weather service, you could configure the operation as follows:
In your extension of EnsLib.REST.Operation, you specify the remaining parts of the URL by appending the value to the adapter URL property. Then you call one of the following adapter methods depending on what HTTP operation you want to use:
For example, the following extension of EnsLib.REST.Operation calls the weather REST service and provides a city name as a parameter:
Class Test.REST.WeatherOperation Extends EnsLib.REST.Operation

Parameter INVOCATION = "Queue";

Method getWeather(
   pRequest As Test.REST.WeatherRequest,
   Output pResponse As Test.REST.WeatherResponse) As %Status
   try {
      // Prepare and log the call
      // Append the city to the URL configured for adapter
      Set tURL=..Adapter.URL_"?q="_pRequest.City_"&units=imperial"
      // Execute the call
      Set tSC=..Adapter.GetURL(tURL,.tHttpResponse)
      // Return the response
      If $$$ISERR(tSC)&&$IsObject(tHttpResponse)&&$IsObject(tHttpResponse.Data)&&tHttpResponse.Data.Size {
         Set tSC=$$$ERROR($$$EnsErrGeneral,$$$StatusDisplayString(tSC)_":"_tHttpResponse.Data.Read())
      If $IsObject(tHttpResponse) {
         // Instantiate the response object
         set pResponse = ##class(Test.REST.WeatherResponse).%New()
         // Convert JSON into a Proxy Cache Object
         set tSC = ..JSONStreamToObject(tHttpResponse.Data, .tProxy)
         if (tSC){                                 
            // Set response properties from the Proxy Object
            set pResponse.Temperature = tProxy.main.temp_"F"
            set pResponse.Humidity = tProxy.main.humidity_"%"
            set pResponse.MaxTemp = tProxy.main."temp_max"_"F"
            set pResponse.MinTemp = tProxy.main."temp_min"_"F"
            set pResponse.Pressure = tProxy.main.pressure_" mbar"
            set pResponse.WindSpeed = tProxy.wind.speed_" MPH"
            set pResponse.WindDirection = tProxy.wind.deg_" degrees"
            // Convert from POSIX time
            set pResponse.Sunrise = $ZT($PIECE($ZDTH(tProxy.sys.sunrise, -2),",",2),3)
            set pResponse.Sunset = $ZT($PIECE($ZDTH(tProxy.sys.sunset, -2),",",2),3)
       Set tSC=$$$SystemError
   Quit tSC

XData MessageMap

  <MapItem MessageType="Test.REST.WeatherRequest">

The message sent to the operation specifies the city:
Class Test.REST.WeatherRequest Extends (%Persistent, Ens.Util.MessageBodyMethods)
   Property City As %String;
This operation calls the JSONStreamToObject() method and returns a Caché object that makes the elements of the JSON accessible. The message returned by this sample returns the following properties taken from the JSON stream:
Class Test.REST.WeatherResponse Extends (%Persistent, Ens.Util.MessageBodyMethods)
   Property Temperature As %String;
   Property MinTemp As %String;
   Property MaxTemp As %String;
   Property Pressure As %String;
   Property Humidity As %String;
   Property WindSpeed As %String;
   Property WindDirection As %String;
   Property Sunrise As %String;
   Property Sunset As %String;
If you don’t have a business process running you can run and test this and other operations in [Ensemble > Production Configuration] by selecting your operation, navigating to Actions in the Production Settings menu and clicking Test.