Getting Started with the SAP Cloud Platform SDK for iOS – Part 5 – Offline OData

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A mobile application may not always be used in areas where a network connection is present or if it is, it may have high latency. The Offline OData framework enables the application to work against a local database instead of making online requests to read or update data.

The following are some additional sources of documentation on using proxy classes to access OData while offline.
SAPOfflineOData Reference
Developing Offline Applications
Implementing Offline OData in your Application
Handle Error Scenarios with Offline OData (Tutorial)
Offline OData in iOS Native Mobile Interactive Tutorials

The following steps demonstrate how to enable offline reads without network connectivity.

1. Add the below import to the top of ViewController.swift.

   import SAPOfflineOData

2. Add the following method.

       func getProductsOffline(_ serviceRoot: URL, _ urlSession: SAPURLSession) {
           var storeParams: OfflineODataParameters = OfflineODataParameters()
           storeParams.storeName = "ESPMOfflineDB"
           do {
               let oDataProvider = try OfflineODataProvider(serviceRoot: serviceRoot, parameters: storeParams, sapURLSession: urlSession)
               let espmContainer = ESPMContainer(provider: oDataProvider)
               let productsDQ = OfflineODataDefiningQuery(name: "ProductsQuery", query: "Products", automaticallyRetrievesStreams: false)
               try oDataProvider.add(definingQuery: productsDQ)
               oDataProvider.open(completionHandler: { ( _ error: OfflineODataError? ) -> Void in
                   if (error == nil) {
                       print("Store successfully opened")
                       espmContainer.fetchProducts() { products, error in
                           guard let products = products else {
                               self.logger.error("Error fetching products:  \(error!.localizedDescription)")
                               return
                           }
                           print("Offline:  got \(products.count) products and the first product name is \(products[0].name!)")
                           //try! oDataProvider.close()
                       }
                   } else {
                       self.logger.error("Store open failed")
                   }
               } )
           }
           catch {
               logger.error(error.localizedDescription)
           }
       }

3. In the buttonPressed method, call the newly added getProductsOffline method after the call to getProducts.

   getProductsOffline(serviceURL, myContext.sapURLSession)

4. Run the example with a network connection. The first time the store is opened, a database will be created on the server and downloaded to the device.The expected output is shown below.

   Button pressed 1 times
   Currently connected by WiFi
   Got 123 products and the first product name is Surround Sound
   Store successfully opened
   Offline:  got 123 products and the first product name is Gaming Monster Pro
   

5. Turn off Wi-Fi on your Mac if running on a simulator or turn on airplane mode if on a device and press the button again. The expected output is shown below. Notice that the online request fails while the offline request succeeds.

   Button pressed 1 times
   Currently offline with no network connection
   2017-11-11 14:31:21.046636-0500 GettingStarted[48051:2665101] TIC TCP Conn Failed [2:0x608000362280]: 1:50 Err(50)
   2017-11-11 14:31:21.047412-0500 GettingStarted[48051:2665101] Task FB2FEB2D-4415-4830-B894-B1027975BDA1. 2 HTTP load failed (error code: -1009 [1:50])
   2017-11-11 14:31:21.047595-0500 GettingStarted[48051:2666620] Task FB2FEB2D-4415-4830-B894-B1027975BDA1. 2 finished with error - code: -1009
   Error fetching products:  Optional(HTTPError: The Internet connection appears to be offline.)
   Store successfully opened
   Offline:  123 products and the first product name is Gaming Monster Pro
   

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