ex5_calc_view_as_odata_srv.md

Exercise 5: Expose Calculation Views as an OData Service

In this last exercise, we will expose all our calculation views as individual entity sets of an OData service.

Exercise Steps

1. Right-click on the project name and select New -> NodeJS Module

   

2. Call the module all_routes and press Next

3. You can give the module a description if you wish, but the important option here is to switch on the "Enable XSJS Support" flag.

   

   Press "Finish"

4. Open the file all_routes/server.js and change the value of the redirectUrl property on line 10 to the following:

   "/xsodata/AllRoutes.xsodata?$format=json"

   The entire options object should now look like this:

   var options = {
       anonymous : true, // remove to authenticate calls
       redirectUrl : "/xsodata/AllRoutes.xsodata?$format=json"
   };

   Notice here that we have told the xsjs server to redirect incoming requests to an .xsodata file called AllRoutes.

   We now need to create this file.

5. Right-click on the all_routes/lib folder and create a new folder called xsodata

6. Right-click on the new all_routes/lib/xsodata folder and create a new file called AllRoutes.xsodata

   

7. The objective here is to expose each calculation view as a separate entity set within an OData service. Enter the following CDS definition into the file AllRoutes.xsodata:

   service {
     "route0stop"  as "DirectFlights" keys("ID") parameters via entity;
     "route1stop"  as "OneStop"       keys("routeText", "airlineText") parameters via entity;
   }
   

   This declaration does the following:

   1. The OData service name is derived from the filename. In this case AllRoutes.

   2. Each calculation view is exposed as an entity set within this service using this syntax:

      <calculation view name> as <entity set name>

   3. The keys("ID") part is needed because all OData entities require a key field (even if that key serves no purpose). This statement causes a dummy key field called ID to be generated

   4. parameters via entity causes the input parameters for each calculation view (airportFrom and airportTo) to be made visible through a corresponding entity set ending with the word Parameters

8. Modify the mta.yaml to create a dependency from the all_routes NodeJS module to the spacetravel-db and spacetravel-hdi-container modules.

   1. Open the mta.yaml file

   2. Select the MTA Editor from the tab at the bottom of the editor screen

      

   3. Select the all_routes module

      

   4. Expand the "Requires" section and using the + button, add two dependencies to spacetravel-db and spacetravel-hdi-container. These names will be available from the drop down list.

      Your screen will now look like this

      

9. Right-click on the all_routes NodeJS app name and select Run -> Run as NodeJS Application

   

   When you select this option for the first time, it will take some time to work because an npm install is being run behind the scenes to generate a new NodeJS application. This app is then deployed to the SAP Cloud Platform. Running this option a second time is always much quicker (unless you change something like the package.json file)

10. Once the build and deploy has finished, at the bottom of the SAP Web IDE screen, you will see a message saying "Application is running" and above, you will see the URL to the running app.

    

11. Click on this URL and you will see running app in a new browser tab

12. Due to the fact that in server.js we redirected the request to /xsodata/AllRoutes.xsodata?$format=json, we immediately see following output:

    {
      "d": {
        "EntitySets": [
          "DirectFlights",
          "OneStop",
          "DirectFlightsParameters",
          "OneStopParameters"
        ]
      }
    }
    

    Notice that each of our entity sets has a corresponding Parameters entity set. So in order to read some data from a calculation view, we must do so using a Parameters entity set.

13. Here we will search for direct flights from London Heathrow to New York John F. Kennedy. To invoke this search, change the URL to the following:

    xsodata/AllRoutes.xsodata/DirectFlightsParameters(airportFrom='LHR',airportTo='JFK')/Results

    The general pattern of the URL is shown in this table

    URL Segment	Meaning
    xsodata/AllRoutes.xsodata	The OData service name
    DirectFlightsParameters	The entity set name
    (airportFrom='LHR',airportTo='JFK')	The search predicate
    /Results	The entity set name containing the search results

14. Invoking the above search will generate search results similar to the following

    {
      "d": {
        "results": [
          {
            "__metadata": {
              "uri": "https://wham6fjzs2eaoz5tt-hana-all-routes.cfapps.eu10.hana.ondemand.com/xsodata/AllRoutes.xsodata/DirectFlights('LHRJFKAA')",
              "type": "default.DirectFlightsType"
            },
            "ID": "LHRJFKAA",
            "DISTANCE": 5541,
            "STARTINGAIRPORT_IATA3": "LHR",
            "DESTINATIONAIRPORT_IATA3": "JFK",
            "AIRLINE_IATA2": "AA",
            "EQUIPMENT_AIRCRAFT1_EQUIPMENTCODE": "77W",
            "EQUIPMENT_AIRCRAFT2_EQUIPMENTCODE": "777",
            "EQUIPMENT_AIRCRAFT3_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT4_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT5_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT6_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT7_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT8_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT9_EQUIPMENTCODE": null,
            "routeText": "LHR->JFK"
          },
          {
            "__metadata": {
              "uri": "https://wham6fjzs2eaoz5tt-hana-all-routes.cfapps.eu10.hana.ondemand.com/xsodata/ AllRoutes.xsodata/DirectFlights('LHRJFKAF')",
              "type": "default.DirectFlightsType"
            },
            "ID": "LHRJFKAF",
            "DISTANCE": 5541,
            "STARTINGAIRPORT_IATA3": "LHR",
            "DESTINATIONAIRPORT_IATA3": "JFK",
            "AIRLINE_IATA2": "AF",
            "EQUIPMENT_AIRCRAFT1_EQUIPMENTCODE": "76W",
            "EQUIPMENT_AIRCRAFT2_EQUIPMENTCODE": "764",
            "EQUIPMENT_AIRCRAFT3_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT4_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT5_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT6_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT7_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT8_EQUIPMENTCODE": null,
            "EQUIPMENT_AIRCRAFT9_EQUIPMENTCODE": null,
            "routeText": "LHR->JFK"
          }
        <snip>
        ]
      }
    }
    

Previous Exercise

</exercise>