Now, you need to change the Online behavior to Offline usage. Open the ESPMContainerDataAccess.swift file under Demo > Model.

Add the import declaration for SAPOfflineOData just below the already existing SAPOData import declaration:

// other imports
import SAPOfflineOData

class ESPMContainerDataAccess {
    // code
}

Since the data service is used offline, you need to change the service declaration for offline usage. In order to do so, change the type of the ESPMContainer variable service to OfflineODataProvider:

var service: ESPMContainer<OfflineODataProvider>

To instantiate the above service, an offline OData provider is needed. Below the field service, add a field offlineODataProvider of type OfflineODataProvider:

var offlineODataProvider: OfflineODataProvider

Replace the init() initializer with the following:

init(urlSession: SAPURLSession) {
    var offlineParameters = OfflineODataParameters()

    offlineParameters.storeName = "OFFLINE_STORE"
    offlineParameters.enableRepeatableRequests = true

    // create offline data provider
    self.offlineODataProvider = try! OfflineODataProvider(
        serviceRoot: Constants.appUrl,
        parameters: offlineParameters,
        sapURLSession: urlSession
    )

    // define offline defining query
    try! self.offlineODataProvider.add(
        definingQuery: OfflineODataDefiningQuery(
            name: CollectionType.products.rawValue,
            query: "/\(CollectionType.products.rawValue)?$top=5",
            automaticallyRetrievesStreams: false
        )
    )

    self.service = ESPMContainer(provider: self.offlineODataProvider)
}

To initialize the offline OData provider, you first set up an instance of OfflineODataParameters. With this instance, you set the custom header, provide a name and path for the offline store, and ensure an OData request is applied only once in case of multiple executions.

Then, a reference to the offline data provider is set to the field offlineODataProvider.

The line which defines the offline defining query is used for the Products defining query you created in the previous tutorial.

Finally, the service field is set to reference the ESPMContainer based on the offline data provider.

Try to build and run the app. If all goes well, the build will succeed and you will be asked to enter your SAP Cloud Platform mobile service for development and operations login credentials at the authentication screen. Once logged in, click on any of the entities to show the master data. Most likely you will receive the following response:

This error is shown because in order to perform any operations in the offline OData store, you first need to open it. And after you have performed the operation, you need to close the store again.

First, we add a new field which holds the state of the store, whether it’s open or not. Open class ESPMContainerDataAccess, and locate the line var service: ESPMContainer<OfflineODataProvider> you wrote at step 5. Just below it, add the following boolean field:

var isStoreOpened = false

Locate the executeRequest<T> method which returns an array [T], and replace its implementation with the following:

private func executeRequest<T>(_ request: @escaping(DataQuery) throws -> [T],
                                 completionHandler: @escaping([T]?, Error?) -> Void) {
    DispatchQueue.global().async {

        if (!self.isStoreOpened) {

            // try opening the store
            self.service.open { error in
                guard error == nil else {
                    self.logger.error("Offline store could not be opened", error: error)
                    return;
                }

                // set flag indicating store is open
                self.isStoreOpened = true

                // download data
                self.service.download { error in
                    guard error == nil else {
                        // in case of error, close store and reset flag
                        self.logger.info("Could not download store", error: error)
                        self.close()
                        self.isStoreOpened = false
                        return
                    }

                    let query = DataQuery().selectAll().top(20)

                    do {
                        // perform query
                        let result = try request(query)
                        completionHandler(result, nil)
                    } catch let error {
                        self.logger.info("Error happened in the downloading process. Error: \(error)")
                        completionHandler(nil, error)
                    }

                    // once finished, close store and reset flag
                    self.close()
                    self.isStoreOpened = false
                }
            }
        }
    }
}

The code above looks a bit more complex compared to the original implementation of the method. This is because the executeRequest method now also takes care of the opening of the store, downloading of the store and closing the store, each with their error handlers and fallbacks.

In addition, a method or function generally should perform only one single task (the “single responsibility” principle, the first and most important principle of the SOLID object-oriented design guidelines), in this case, execute the request. But to get a better understanding of the flow of the code, it is chosen to combine the above multiple responsibilities into one method.

Deploy your application to your iOS device, and once loaded, log on to it.

Switch on Airplane mode, and try open a collection and an entity. It should work without errors: